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6

Teacher’s ManualScience OrbitThe Physics

Kishwar Raza

(An imprint of New Saraswati House (India) Pvt. Ltd.)New Delhi-110002 (INDIA)

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(An imprint of New Saraswati House (India) Pvt. Ltd.)

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Second Floor, MGM Tower, 19 Ansari Road, Daryaganj, New Delhi-110002 (India) Phone : +91-11-43556600Fax : +91-11-43556688E-mail : [email protected] : www.saraswatihouse.comCIN : U22110DL2013PTC262320Import-Export Licence No. 0513086293

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First published 2018

TM Code: 2017007000110

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The purpose of The Science Orbit series (3 to 8) teacher’s resource pack is to empower teachers to make classroom teaching a holistic experience. It will enable teachers to explain the chapters in the most effective way, which will not only impart knowledge, but also ignite interest in the minds of young learners towards the subject. A wide array of resources complement these manuals, which makes learning an interesting process instead of a routine chore.

Teacher’s Manual

Teacher’s Manual resources have been carefully prepared with an aim to make the process of teaching and learning interesting and intriguing for the teachers and learners alike. It comprises detailed lesson plans and answers to the coursebook along with solved worksheets and model test papers. These have been prepared keeping in mind the explanation of the concepts and the level appropriateness of the topics. Easily available teaching aids are used to make teaching and learning an interactive and lucid process. The lesson plans give a topic-wise explanation of each chapter. Its components are:

– Warm-up section guides the teacher to start the topic in an interesting way.

– Learning objectives give the list of measurable aims of each chapter, which should be achieved after teaching the chapter.

– Concept explanation gives a detailed method of explaining the important concepts of the chapter using various teaching aids.

– Reinforce section allows the teacher to check the progress of the concepts learned by the students with the help of textual questions and worksheets and allows them to revisit and revise the concepts, if required.

– Explore section helps the learners to do various activities, often taking them beyond their classroom learning.

App-based Digital Store

Digital offerings comprise digital resource embedded e-book, 2D and 3D animations, videos, interactive activities, slideshows, educational games, test generator and teacher’s manual.

Web Support

The web support consists of worksheets, model test papers, and answers to worksheets and model test papers. These would help teachers in assessing students on the concepts taught in the class.

Preface

Contents

1. Matter 5

2. Measurement 12

3. Force 21

Model Test Paper 1 30

4. Energy 32

5. Light 40

6. Magnetism 48

Model Test Paper 2 57

55

Learning Objectives

Students will be able to: understand and defi ne matter and its composition

understand and defi ne the states of matter

distinguish between solid, liquid and gas

1 Matter

Warm-upPicture cards of various states of matter such as water, steam escaping from a kettle to be shown to students.

A table, marbles, fi sh swimming in water, oil, infl ated balloon, etc. also to be shown to students.

They should be asked to classify the three states of matter under three different headings. Thus, students are reminded of the three states of matter.

Concept ExplanationShow ice, water and boiling water producing steam in different containers to introduce the topic.

Matter; Composition of Matter, Kinetic Theory of matterRead the related sections from the book.

Defi ne matter, atoms, and molecules.

Explain atoms of different elements are different and each atom has its own specifi c property.

Explain the kinetic theory of matter.

Ask the students to answer the related questions from the Part II of the Exercises.

States of Matter; Differences between Solids, Liquids and GasesExplain the three fundamental states of matter.

Read the related sections from the book.

Take a glass jar completely fi lled with plastic balls. Place a hair dryer at the mouth of the glass jar. The light, plastic jars barely show any movement.

Similarly, in two more glass jars, place fewer plastic balls representing liquid and gas. The glass jar showing gas had the least number of balls.

Air was blown into each of the jars. Plastic balls in the liquid glass jar showed movement but there was little space between the balls. Maximum movement was shown by the glass jar representing gas as the balls had a lot of space.

Explain the arrangement of particles with the help of pictures of steam coming out of a steam engine (gas), water in a glass (liquid) and a tree or furniture at home (solid).

Ask the students to answer the related questions from the Part II of the Exercisse.

66

ReinforceTo reinforce, read the Summary and Glossary sections from the book.

Ask the students to do Pause and Do section from the book.

Use Part I of the Exercises to conduct a quiz contest in the class.

Explore To explore, ask the students to do the Learning Zone section from the book.

77

Worksheet 1

1. Fill in the blanks.

a. All ________________ is made up of very small particles.

b. ________________ are the basic unit or building block of matter.

c. A ________________ has a defi nite shape, that is diffi cult to change.

d. ________________ cannot be compressed at all.

e. ________________ are always in a state of rapid, random motion.

2. State True or False.

a. Liquids can fl ow because their molecules have least _________ intermolecular space.

b. Liquids have a fi xed shape but not a fi xed volume. _________

c. Particles of a solid vibrate about their mean position. _________

3. Name the following.

a. The ability to be contained in a small volume ________________

b. The state of matter that has a fi xed shape and volume ________________

c. The state(s) of matter that can fl ow ________________

d. The word that means indivisible in Greek ________________

4. Answer the following questions.

a. Give two points of differences between a solid and a gas.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

b. Explain the kinetic theory of matter in brief.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

88

Worksheet 2

1. Choose the correct option.

a. The word atoms means,

i. Smallest particle ii. Building block iii. Indivisible iv. Similar

b. LPG is an example of:

i. Solid ii. Liquid iii. Gas iv. Both (ii) and (iii)

c. The state of matter that is highly compressible is

i. gas ii. solid iii. liquid iv. Both (a) and (c)


a. Both liquids and gases can fl ow. _________

b. Mercury is a solid. _________

c. Gases take the shape of the container in which they are kept. _________

3. Match the columns.

a. Ice i. Energy possessed by a molecule due to its motion.

b. Matter ii. Solid state of matter

c. Wood iii. Anything that occupies space and has weight

d. Kinetic energy iv. Cannot be compressed.


a. What is the arrangement of particles in liquid?

_____________________________________________________________________

_____________________________________________________________________

b. Give the difference between solids and liquids with respect to intermolecular space.

_____________________________________________________________________

_____________________________________________________________________

99

Answers to Coursebook

PART 1

A 1 (c) 2. (c) 3. (c) 4. (b)

5. (c) 6. (c) 7. (a)

B 1. wood 2. petrol

3. carbon dioxide 4. zig-zag

5. gases 6. most

7. gas

C 1. True 2. False 3. True

4. True 5. True

D 1 (c) 2. (d) 3. (a) 4. (e)

5. (b)

PART 2

A 1. Iron and wood

2. Petrol and water.

3. Oxygen and carbon dioxide

4. Soft rubber

5. Spring or elastic band

6. LPG or Butane, propane.

B. 1. Matter is anything that occupies space and has weight.

2. Solid, liquid and gas. Steel, petrol and Hydrogen.

3. A gas has no defi nite shape. It can be highly compressed.

4. The force of attraction that between molecules of a liquid is greater than in gases.

5. Particles of a solid are tightly packed with very little intermolecular space between them.

6. Force of attraction between molecules of a substance is called intermolecular force.

C. 1. Matter is composed of tiny particles called molecules. Molecules are in a state of random motion which depends upon the kinetic energy possessed by individual

molecules. There is intermolecular space between molecules. The force of attraction between molecules decreases with an increase in the distance between molecules.

2. Solids:

• Have a defi nite shape and volume.

• Very little intermolecular space between molecules.

• Force of attraction between molecules of a solid is maximum.

Liquids:

• No defi nite shape, takes the shape of the container.

• There is space between molecules of a liquid, they move move past one another, so a liquid can fl ow.

• There exists force of attraction between molecules of a liquid much less than solids but greater than gases.

3. • Liquids and gases do not have a defi nite shape.

• Liquids and gases can fl ow because molecules can move past one another.

• A gas can be compressed easily, whereas a liquid can also be compressed with a greater degree of effort.

4. An atom is the smallest particle of an element which is indivisible.It is the basic building block of all matter. Atoms of the same element combine to form molecules.

5. A gas can be compressed because there is large space between molecules of a gas.

D 1. Intermolecular space: The distance between the molecules of a particular state of matter.

Intermolecular space is maximum between molecules of a gas and minimum between molecules of a solid.

1010

2. Molecule: Two or more atoms combine to form a molecule. A molecule is the smallest particle of an element which can exist independently.

3. Compression: When there is large intermolecular space between the particles of matter such as gas, they can be compressed easily. Whereas liquids which have comparatively less intermolecular space cannot be compressed with ease.

4. Atom: An atom is the smallest particle of an element which is incapable of independent existence.

E. 1. An empty vessel contains hundreds and thousands of tiny molecules of gas which though invisible to us, are in a state of constant, random motion.

2. There is less intermolecular space between molecules of a liquid, hence liquids cannot be compressed easily.

3. There is large intermolecular space between molecules of a gas, hence they can be compressed easily. For example, fi lling air in a cycle tyre tube, blowing a balloon, etc.

LEARNING ZONE

Picture based questions

1. (a) Solid (b) Liquid (c) Do it yourself.

2. (a) gas

(b) Solid: Rock, road, tree; Liquid: Water; Gas: Air

3. Gas and liquid

Think and answer

1. Onions contain a liquid, which has lots of sulphur in it. When we cut an onion, this liquid is released. It evaporates very fast. When the liquid gases reach our eyes, it causes irritation and sends signals to our tear gland to produce tears, so that the tears can wash away the irritant from our eyes.

2. It happens because at high temperature, the rate of diffusion increases. So, the particles of the smell of the incence stick diffuse faster with air molecules and spread quickly in all the rooms of the house.

3. It happens because of the phenomenon of diffusion. The particles of food get mixed with the air present in the room when we open up our lunch box in the classroom.

4. Hydrogen → Water → Sand

5. We all know that air is a gas. The gas molecules are loosely packed and there are intermolecular spaces and the molecules move around. So when we move our hand freely in air the molecules are disturbed and and hence move and there is space for us to move our hands but in solids the molecules are packed tightly with no intermolecular space for the movement of the molecuels of the solid. Thus we can only break the wood to make space to move our hand as we cannot push the molecules away, and for this we need to be a karate expert.

Answers to Worksheets

WORKSHEET 1

1. a. Matter b. Atom c. Solid

d. Solid e. Molecules

2. a. False b. False c. True

3. a. Compression

b. Solid

c. Liquid and gas

d. Atomos

4. A solid has a defi nite shape and volume.

There is no intermolecular space between the molecules in solids.

Gases have neither a defi nite shape nor a defi nite volume.

1111

There is large intermolecular space between molecules in gases.

b. Matter is composed of tiny particles called molecules. Molecules are in a state of random motion which depends upon the kinetic energy possessed by individual molecules. There is intermolecular space between molecules. The force of attraction between molecules decreases with an increase in the distance between molecules.

WORKSHEET 2

1. a. iii b. iii c. ii d. i

2. a. True b. False c. True

3. a. ii b. iii c. i

4. a. Particles or molecules are close together with no regular arrangement. The molecules in a liquid move about freely in random, zig-zag motion throughout the bulk of the liquid.

b. Molecules in solids are closely packed whereas in liquids molecules are loosely packed.

There is no intermolecular space between molecules in solids. Liquids molecules have enough intermolecular space to move freely. They move past one another hence liquids fl ow.

1212

Learning Objectives

Students will be able to: understand physical quantities such as length, mass, time and temperature and their

units of measurement.

understand the need for accurate and precise measurement, SI system of units and inter conversion of units that is followed all over the world.

measure area by using formulae and by the use of graph paper, fi nding average and estimation of physical quantities to be taught to the student.

2 Measurement

Warm-upAsk the tallest student of the class to measure the length of the teacher’s table using his/her handspan.

Suppose he/she measures it as 6 handspans.

Again call another student and ask him/her to do the same.

Suppose he/she measures it as 7 handspans. The students are confused.

Next day, the teacher brings a measuring tape and asks the students to measure the length of the table. Let it be measured as 120 cm.

Next, the teacher takes a glass full of water and asks the students, how much water is there in the glass. The students may not give proper or same answers.

So, the teacher pours the water in a measuring jar and says that the water measures 250 mL.

The teacher now explains the need for accurate and precise measurement of objects in daily life.

Thus whether it be length, mass, area, time or temperature, an accurate measurement of these physical quantities is necessary. Each of these quantities needs units to measure.

Thus those units are used for measurement which are accepted all over the world. They are named as SI units.

Read the Warm-up section from the book and do the activity given in this section.

Concept ExplanationMeasurement, Need for Standard Units of Measurement, Convention while Writing SI unitsIn a cardboard box, the let the teacher kepp objects like a spring balance, small weights of 50 g, 10 g, 20 mg, 5 mg, a clinical thermometer, a laboratory thermometer, digital clock, analog clock, a ruler, a measuring tape and a graph paper.

She picks each object one by one and asks the students the names of the objects, the physical quantities and the units they measure.

1313

Thus whether it be length, mass, area, time or temperature, an accurate measurement of units is required.

These physical quantities are necessary. Each of these quantities needs units to measure them. Thus units were used which were accepted all over the world. They were named SI units. Read the related sections from the book.


Measurement of Length; SI units of Length; Instruments used to Measure Length• Explain to the students that length is a

measure of the distance between two points.

• Read the related section from the book.

• Explain the SI unit of length to the class. Use the tables given to explain the relation between different units of lengths.

• To reinforce ask the students to do the Pause and Do section from the textbook.

• Demonstrate how to measure length of objects using ruler.

• Conduct activities and experiment given on the page 23 for better understanding of the concept.

• Now demonstrate how to measure length of the objects using measuring tape.

• Ask students to do Pause and Do section given on page 24.

Measurement of Mass; SI units of Mass; Instruments used to Measure Mass• Explain to the students that mass is

the amount of matter contained in a substance.


• Explain the SI unit of mass to the class.

• Explain the relation between different units of mass.

• To reinforce ask the students to do the Pause and Do section from the textbook.

• Demonstrate how to measure mass of the objects using a beam balance and a physical balance.


Measurement of Time; Instruments Used to Measure Time, 12- hour and 24-hour format in Time• Explain that time is defi ned as the interval

between two events.


• Explain the units of time to the class.

• Demonstrate how to read and write time using different clocks.

• Conduct activities and experiment given on the pages 28 and 29 for better understanding of the concept.


Measurement of Temperature• Defi ne temperature is the measure of the

degree of hotness or coldness of a body.


• Explain the units of temperature to the class.

• Demonstrate how to read and calculate temperature using a clinical or a laboratory thermometer.

• Conduct experiments given on page 31 for better understanding of the concept.


• Ask the students to answer the related questions from the Part II of the Exercise.

Measurement of Area; Approximation; Average• Defi ne the total surface occupied by an

object is called its area or surface area.

1414


• Explain the units of the area to the class.

• Explain how to fi nd area of regular shape using graph paper and by using formulae.


• Conduct activity given on the page 34 to fi nd the average height.

• Use examples given in the related section for better understanding of the concept.

• Ask the students to answer the related

questions from the Part II of the Exercises.



Explore To explore, ask the students to do the Learning Zone section from the book.

1515

Worksheet 1


a. Units that have a fi xed quantity and do not vary are called ________________.

b. To measure larger lengths, larger units such as ________________ are used.

c. The SI unit of temperature is ________________.

d. A laboratory thermometer has markings from ______________ to ______________.

e. The ________________ hour clock is used in railways and computers.


a. The ability to be contained in a small volume ________________

a. A thermometer to measure the temperature of the human body________________

b. Rounding off values to the nearest digit ________________

c. A watch which shows time in digits ________________

d. A fl exible ruler that can measure large distances ________________


a. Standard units are more accurate than hand span, pace and footstep. _______

b. For precise and accurate measurement of mass, a beam balance is used. _______

c. A second is a fraction of the mean solar day. _______

d. The lowest temperature on the Kelvin scale is –273K. _______


a. What is the normal temperature of the human body in °C?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

b. Why is there a need for accuracy in measurement? Give two points.

_____________________________________________________________________

_____________________________________________________________________

1616

Worksheet 2

1. Choose the correct option:

a. 1 km = __________ m

b. 1 inch = __________ cm

c. 1 metric tonne = __________ kg

d. 1 hectare = __________ m2

2. Answer the following questions:

a. What is parallax error? How can it be removed?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

b. Give the difference between an analog and a digital watch.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

3. Solve the followings.

a. Calculate the area of a circle of radius 6 cm using a graph paper. Answer approximately.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

b. The fl ight for Mumbai will depart at 20:05 hours. What is the time of fl ight in12-hour clock.

_____________________________________________________________________

_____________________________________________________________________

1717


PART 1

A 1 (c) 2. (d) 3. (b) 4. (c)

5. (b) 6. (d) 7. (a) 8. (b)

B 1. Kelvin 2. Time

3. Simple pendulum 4. Beam balance

5. Measuring tape 6. Parallax error

7. Compound units 8. Metre

9. Stopwatch

C 1. False 2. True 3. False

4. True 5. True 6. True

7. True 8. False 9. False

10. True

D 1. Clinical thermometer

2. Laboratory thermometer

3. Physical balance

4. Beam balance

5. Electronic balance

6. 24 hour clock

7. Digital watch

PART 2

A 1. Physical quantities such as length, mass, time and temperature have to be measured with respect to some fi xed quantities which are known as units.

2. Units that have a fi xed quantity and do not vary are called standard units.

3. Length is a measure of the distance between two points.

4. Centimetre and millimetre.

5. Micrometre and millimetre

6. Inches, centimetres, millimetres

7. Kilogram

8. A ruler and a thread

9. Interval between two events is time

10. Sand glasses and water clocks

11. 320F

B. 1. The total surface occupied by an object is called its area.

2. ½ x base x height

3. Accuracy in measurement of physical quantities is required so that measurement does not vary and remain the same everywhere. Medicines, weight of precious metals are measured accurately everywhere.

4. An average reading gives a general idea of the value of most of the numbers in a group.

5. Sugar will be placed on the left pan, standard weights are placed on the right pan. The balance is held such that the beam is horizontal. The total of all the standard weights gives the mass of sugar.

6. A thread is placed all along the length of the curved line. A ruler is then used to measure the length of the thread in cm. This is the length of the curved line.

C. 1. A clinical thermometer is used to measure the temperature of a patient’s body. It has markings from 35 °C to 42 °C in the Celsius scale and 95 °F to 108 °F on the Fahrenheit scale.

2. The following precautions should be taken while using a ruler:

(a) The 0 point of the ruler should coincide exactly with the starting point of the object.

(b) The ruler should be placed exactly along the length of the object to be measured.

(c) Rulers with broken edges and diffused markings should not be used.

(d) The eyes of the person should be placed exactly in front or vertically above the reading.

1818

3. To measure the time between the start and the stop of an event, stop watches are used. These can be started and stopped as per the need.

4. To fi nd the area of a rectangle, keep the shape on the graph paper. Mark the outline.

Now, count the number of square shapes that are within the outline. The number of complete squares and greater than half squares gives the area of the rectangle directly.

5. Estimation means getting a value as good as or nearly equal to a particular value. Such values are rounded off to the nearest digit.

6. The 24- hour clock is a type of time keeping method, where the day is divided into 24 hours from one midnight to the next. In this system, the day begins at midnight (00:00 hours).

12:00 is mid-day and 24:00 is used to signify the end of the day (midnight).

7. An electronic balance is used for precise and accurate measurement of the mass of an object. It can measure a mass as small as 1 mg, as well as large masses of the order of quintals.

D. 1. Submultiples are smaller units of a meter to measure smaller lengths.

2. Metre is the SI unit of length. It is defi ned as the distance between two points on a rod made of an alloy of platinum-irridium kept at 0 °C in the International Bureau of Weights and Measures at Sevres near Paris.

3. A physical balance is a highly sensitive version of the beam balance. It is used in the science laboratories for accurate measurement of chemicals also to measure precious metals like gold and silver.

4. The Fahrenheit scale invented by Gabriel Daniel Fahrenheit shows the freezing point of water at 32 °F and the boiling point of water at 212 °F. It has 180 divisions.

5. Standard units: Units that have a fi xed quantity and do not vary are called standard units.

Length, mass, time, temperature, etc. are called standard units.

E. (a) A clock or watch that has a numbered dial and moving hands is an analog clock.

A watch that shows time in digits is called digital clock.

(b) A clinical thermometer is used to measure the temperature of a patients body. It has markings from 35 °C to 42 °C in the Celsius scale and 95 °F to 108 °F on the Fahrenheit scale.

Laboratory thermometer: It is used to measure temperature of ordinary objects, also to fi nd the boiling and freezing point of water. The stem has markings from–10 °C to 110 °C.

(c) Beam balance: It is used to measure the mass of ordinary everyday articles like vegetables, rice, sugar, etc.

Physical balance: It is a highly sensitive balance used to measure chemicals in the science laboratory, also to measure the weight of precious metals like gold and silver.

(d) Standard units: Units that have a fi xed quantity and do not vary are called standard units. For example, metre, kilogram, second and Kelvin.

Non-standard units: Non-standard units do not give an accurate measurement, but vary from person to person and place to place. For example, cubit, hand-span, foot-span, pace, etc.

(e) Ruler: A ruler is used to measure small lengths. It has markings in inches, cm and mm.

It measures straight objects or straight lines.

Measuring tape: A measuring tape is a fl exible ruler. It consists of a ribbon of cloth, plastic, fi bre-glass or metal strip with markings in cm or mm on it. Tapes

1919

are available ranging from 1 m to 100 m in length.

F. (a) Newton

(b) Ampere

(c) Beam balance

(d) Physical balance

(e) Hotness

(f) Clinical thermometer

G. 1. Area in SI unit = 2000/100 × 100

= 0.2 m2

2. (a) 2.5 metric tone

(b) 1.5 quintal

(c) 4.53 kg

(d) 2.5 kg

(e) 10 g

3. (a) 195s

(b) 18125 s

4. (a) 4:20 pm; 9:45 am

(b) 3:15 pm; 5:05 pm

(c) 12:35 pm

(d) 8:10 am

(e) 11:02 am

5. (a) 1100 (b) 1200 (c) 2400

(d) 1820 (e) 0315 (f) 2147

(g) 2305 (h) 0245

6. Area of the triangle = ½ × base × height

= ½ × 10 × 5

= 25 cm2

7. Weight of each piece = 7 g

LEARNING ZONE


1. (a) A → Physical balance,

B → Electronic balance,

C → Beam balance

(b) Physical balance: It is used in science laboratories for the accurate measurement of chemicals.

Electronic balance: It is used for precise and accurate measurement of the mass of an object.

Beam balance: It is used to measure the weight of an object.

(c) No

(d) A

(e) C

2. (a) A → Stopwatch, B → Analog,

C → Digital

(b) A

(c) B and C

(d) A

3. Do it yourself.

Think and Answer

1. kilometre

2. No

3. No, because it can measure the temperature from 35°C to 42°C.

4. A clinical thermometer measures the maximum temperature of the human body due to the expansion of the mercury in the bulb, which fl ows past a kink in the column and rises in the graduated stem, to read the highest body temperature. Once it is removed from the body, the mercury stays at that level, and does not fall because it cannot fl ow back into the bulb as the kink prevents the back fl ow. It has to be shaken vigorously, as you know, for us to get the mercury back; then it is ready to take the temperature again.

2020


WORKSHEET 1

1. a. standard units

b. kilometre

c. Kelvin

d. –10 °C to 110 °C

e. 24-hour clock

2. a. Clinical

b. Approximation

c. Digital clock

d. Measuring tape

3. a. True

b. False

c. True

d. False

4. a. 37 °C

b. Accuracy in measurement of physical quantities is required so that measurement is same all over the world.

Medicines, weight of precious metals are measured accurately everywhere.

WORKSHEET 2

1. a. 1000 m

b. 2.54 cm

c. 1000 kg

d. 10,000 m2

2. a. An error caused due to improper positioning of eyes while taking a reading is called parallax error. It can be removed by positioning the eye vertically above the mark or keeping the eye exactly in front of the reading.

b. An analog watch or clock is a normal watch with a numbered dial and moving hands. A digital watch shows the time in digits.

3. a. Area of the circle = Number of squares enclosed within the fi gure. = 113 cm2

b. 8:05 pm

2121

Learning Objectives

Students will be able to: defi ne force and its effects.

understand advantages and disadvantages of friction.

understand and defi ne force of friction.

3 Force

Warm-upTake a spring balance and hang a 20 g weight at one end. The spring stretches as the pointer moves on the scale.

Keep a plastic ball on the table and push it. It moves. Try to move a football with the same force as applied earlier. It does not move.

Force of friction is stopping the heavier ball from moving.

Take a toy car. Push it on a glass surface. It moves a longer distance.

The above activities help students to understand the defi nition of force and effects of force in everyday life.

Read the Warm-up section from the book.

Concept ExplanationForce; Effects of force; Force of friction• Ask students to do the following activities:

(a Stretch a rubber band.

(b) Push a stationary car.

(c) Squeeze a toothpaste tube

(d) Kick a football

(e) Pull a drawer

(f) Push a loaded trolley

• Read the related sections from the book.

• Defi ne force and explain the effect of force on objects.

• Use activity given on page 43 to make students understand the concept in a better way.

• Read the section force of friction from the book.

• Try to cycle fi rst using a new tyre and then using an old tyre.

• Compare the motion of the cycle in both the cases.

• Cycle on a wet road and then on a dry road. What is the difference? Is cycling on a wet road easier?

• The students understand the concept of friction and its role in everyday life.

• Defi ne friction acts in a direction opposite to the direction in which an object tends to move.

• To reinforce ask the students to do the related Pause and Do section and activity given on page 45 from the book.

2222

Types of Friction; Advantages and disadvantages of friction; Methods of reducing friction• Read the related sections from the book.

• Defi ne types of friction.

• Explain types of friction such as static, sliding and rolling with the help of activities using rollers and wooden blocks.

• Give example of an old sewing machine that makes noise and does not run smoothly and a well oiled, greased machine that runs smoothly.

• Explain the advantages and disadvantages of friction to the students.

• To reinforce, ask the students to do the related Pause and Do section from the textbook.

• Read the section Methods of reducing fraction from the book.

ReinforceTo reinforce, read the Summary and Glossary section, from the book.

Use Part I of the Exercises to conduct a

quiz contest in the class.

Explore • To explore, ask the students to do the

Learning Zone section from the book.

• To explore more, ask the students to do the following activities.

(a) Take a toy car and push it on a glass surface and then push it on a wooden

surface. Observe on which surface the car covers a longer distance.

(b) Take a wooden block weighing 100 g. Push it on a cemented fl oor. Next fi x rollers below the block and push it. Draw your conclusion.

(c) Release a blunt and a pointed arrow from the bow. Which arrow moves a longer distance?

(d) Make a toy aeroplane with paper and release it from the top steps of your house. Observe how it moves in air resisting air friction.

(e) Spill some water on the fl oor. Can you walk on this fl oor without slipping? Why?

2323

Worksheet 1


a. ________________ can make a stationary object move.

b. ________________ produces heat.

c. Smoother the surface ________________ will be the friction.

d. ________________ and ________________ remain on the wall due to friction.

e. On a carrom board talcum powder is sprinkled to ________________ friction.


a. Friction due to air and water. ________________

b. SI unit of force. ________________

c. Another name given to sliding friction. ________________

d. Special shape of birds and fi shes. ________________

e. The maximum value of frictional force between two surfaces. ________________


a. Sliding friction is less than rolling friction. ________

b. Friction acts in a direction opposite to the direction of motion. ________

c. Friction increases speed. ________

d. When a football stops its speed becomes zero. ________


a. Name two effects of force, with an example for each.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

b. State two ways in which you can reduce friction.

_____________________________________________________________________

_____________________________________________________________________

2424

Worksheet 2


a. Friction is the force that ______________ motion.

b. The surface of a table has many irregularities in the form of ______________ and ______________.

c. Materials that break easily when force is applied are termed as ______________.

d. ______________ and ______________ have naturally streamlined bodies.


a. Vehicles move on roads due to the friction between the brake _________ and the tyre.

b. Polishing rough surfaces can increase friction. _________

c. Use of ball bearings can make a machine work smoothly. _________

d. Kicking a stationary ball can change the direction of motion _________ of the ball.

3. Match the columns.

a. Least area in contact i. Reduces friction

b. Self adjusting friction ii. Change in shape of the body

c. Use of lubricants iii. Static friction

d. Using a spring balance iv. Rolling friction


a. Give two points of difference between rolling and sliding friction.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

b. Explain static friction.

_____________________________________________________________________

_____________________________________________________________________

2525


PART 1

A 1 (d) 2. (a) 3. (d) 4. (b)

5. (c)

B 1. Force 2. Faster 3. Friction

4. Newton 5. Rolling

C 1. True 2. False 3. True

4. False 5. False

D 1. Friction 2. Rolling friction

3. Static friction 4. Friction

5. Fluid friction

PART 2

A 1. A push or a pull acting on an object is called force.

2. A horse pulling a cart.

3. Push a table to change its position, Pushing a loaded cart.

4. Kicking a stationary football.

5. A wooden box being pushed against a cemented fl oor is an example of sliding friction.

6. It can change the speed and direction of a moving object.

B. 1. The force that opposes the motion between two objects moving over each other is called friction.

2. Force can make a stationary object move. It can change the speed and direction of motion.

Force can stop a moving object, and also change the shape of an object.

3. A soft rubber ball can be pressed. An elastic rubber band can be stretched.

4. Rough surfaces have small grooves which are microscopic. When two such rough surfaces move, the grooves and ridges interlock against each other making movement diffi cult.

5. If the object moves towards the right, friction acts toward the left. If you roll a ball on the ground it comes to a stop after some time because of friction.

6. When an object rolls over a surface, the force which opposes rolling motion of the object is called rolling friction.

C. 1. Static Friction: The maximum opposing force between the object and the surface in contact with it, so long as the object remains stationary even on applying an external force, is called static friction.

If we push an object and it does not move. Even on increasing the force the object does not move. When the force increases, the friction between two surfaces becomes maximum, and the object still remains stationary. A slight increase in force can now overcomes static friction and the object begins to move.

2. Advantages of friction:

(a) Vehicles like cars and buses can move on the road due to the force of friction between the tyres and the road, otherwise they would skid.

(b) Brakes in cycles, cars and buses work due to friction.

(c) It is possible to light a matchstick due to friction.

3. Force as a pull: Bullocks pulling a cart.

Force as a push: A vegetable vendor pushing his cart full of vegetables

Force used to change direction: Kicking already moving football in a different direction

Force to change shape: Stretching an elastic rubber band.

4. Rubbing our palms against each other produces heat.

Friction between the moving parts of a machine produces heat.

2626

5. If there was no friction in life, we would not be able to walk, we would slip.

We would not be able to write anywhere.

We would not be able to drive.

D. 1. Force: A push or a pull acting on an object is called force. Force can change direction

of motion and shape or dimensions of an object.

2. Friction: The force that opposes motion between two objects moving over each other is called friction.

3. Sliding friction: When an object slides over another object, such as pushing a big wooden crate against the fl oor, sliding friction is produced.

E. 1. Our palms become warm on rubbing against each other because friction produces heat.

2. The movement of the cycle becomes smooth because rolling friction reduces friction.

3. The bodies of birds and fi shes are streamlined to minimize air friction while fl ying.

4. Rollers are used in luggage trolleys

because rolling friction is less than sliding friction. The luggage can be moved easily with minimum of effort.

LEARNING ZONE


1. Force can change the speed, shape and direction of an object.

2. (a) Since sliding friction is greater than rolling friction.

(b) Yes. Because rolling friction is less than as compare to sliding friction.

Think and Answer

1. Old tyres of vehicles wear out due to friction. Friction between the wheels and the road helps a vehicle to move steadily on the road. Thus, old tyres are more likely to skid on a wet road than new tyres.

2. There is very less friction on a wet fl oor. Thus it is diffi cult to walk on a wet fl oor.

3. There is very less friction on ice. Thus, it is diffi cult to walk on snow but easy to skate on it.

4. Because oil is a lubricant which reduces friction between our hands and glass.

Answers to Assessment 1

A. 1. (a) 2. (c) 3. (c)

4. (c) 5. (a)

B. 1. Matter: Matter is anything that occupies space and has weight.

2. Parallax error: An error caused due to the improper positioning of eyes while taking a reading is called parallax error. The eye should be positioned vertically above the mark on the ruler.

3. Physical quantity: The various quantities, such as length, mass, volume, time and temperature which we can measure are known as physical quantities.

4. Sliding friction: When a body begins to

slide on a surface, the force exerted by the surface on the object is called sliding friction. Sliding friction is less than static friction.

5. Laboratory thermometer: It consists of a glass capillary tube called stem, with a bulb at one end. The bulb is fi lled with mercury. The stem has markings from–10 °C to 110 °C.

C. 1. (c) 2. (e) 3. (d) 4. (a)

5. (b)

D. 1. Petrol, water, etc.

2. Temperature

2727

3. Thermometer

4. Kinetic friction

5. Force

E. 1. Sliding friction: When a body begins to slide on a surface, the force exerted by the surface on the object is called sliding friction. Sliding friction is less than static friction.

Rolling friction: When an object roll over a surface, the force which opposes the rolling motion of the object is called rolling friction. It is less than sliding friction.

2. Clinical thermometer: Doctor’s use a special thermometer called the clinical thermometer to measure the temperature of a patient’s body. This thermometer has markings from 35 °C to 42 °C. The temperature of a healthy person is marked on it as 37 °C .

Laboratory thermometer: It consists of a glass capillary tube called stem, with a bulb at one end. The bulb is fi lled with mercury. The stem has markings from–10 °C to 110 °C. It is mainly used to measure the melting point of ice (0 °C) and boiling point of water (100 °C ).

3. Analog clock: A clock or watch that has a numbered dial and moving hands is an analog clock.

Digital clock: A watch that shows time in digits is called a digital clock.

4. Solids: Solids have a defi nite shape and volume.Very little intermolecular space between molecules. Force of attraction between molecules of a solid is maximum.

Liquids: Liquids have defi nite shape, takes the shape and volume of the container.

There is space between molecules of a liquid, they move past one another, so a liquid can fl ow.There exists force of attraction between molecules of a liquid much less than solids.

5. Electronic balance: An electronic balance is used for precise and accurate measurement of the mass of an object.

It can measure a mass as small as 1 mg, as well as large masses of the order of quintals.

Physical balance: It is a highly sensitive version of the beam balance. It is used in science laboratory for accurate measurement of chemicals.

F. 1. F 2 F 3. T 4. T 5. F

G. 1. Physical quantities such as length, mass and time have to be measured with respect to some fi xed quantity, which is known as units. If we say capacity of a jug is 2 litres, it means 2 is the magnitude and litre is the unit of volume.

2. Ball bearings reduce friction. They change sliding friction into rolling friction which is much less and helps in smooth running of the cycle.

3. Liquids cannot be compressed because there is not much free space between the particles of a liquid.

4. Accuracy is needed to measure physical quantities so that a particular measurement remained the same in different parts of the world. Variation in results would occur if people in different places used different units for measurement of same physical quantity. For example length can be measured in inches, meters and miles and mass in kilograms, pounds and quintals. Hence the need for a standard unit.

5. Time is defi ned as the interval between two events. Clocks, watches and stopwatches are used to measure time.

6. Force can make a stationary object move, stop a moving object and change the direction of a moving object. A ball can be kicked to make it move, a moving ball can be stopped.A football player can change the direction of motion of a moving ball.

7. Friction slows down motion. Friction causes wear and tear of the moving parts of a machine.

H. 1. Matter is composed of tiny particles called molecules. Molecules are in a state of random motion which depends upon the

2828

kinetic energy possessed by individual molecules. There is intermolecular space between molecules. The force of attraction between molecules decreases with an increase in the distance between molecules.

Solids: Have a defi nite shape and volume. Very little intermolecular space between molecules. Force of attraction between molecules of a solid is maximum.

Liquids: No defi nite shape, takes the shape and volume of the container.There is space between molecules of a liquid, they move move past one another, so a liquid can fl ow. There exists force of attraction between molecules of a liquid much less than solids but greater than gases.

Gases: There is very little intermolecular force of attraction between molecules of a gas, molecules are far apart, therefore cannot be compressed.

2. To take the temperature of a patient’s body, the bulb of a clinical thermometer is kept under the tongue or in the armpit of the patient for a minute. The reading is then noted. If the temperature shows above37 °C, the patient has fever.

3. If there is no friction,

(a) we would not be able to write, walk or sit on a chair.

(b) vehicles would not stop on application of brakes if there is no friction.

4. The 24- hour clock is a type of time keeping method, where the day is divided into 24 hours from one midnight to the next. In this system, the day begins at midnight (00:00 hours). 12:00 is mid-day and 24:00 is used to signify the end of the day (midnight).

5. Liquids and gases do not have a defi nite shape and volume.

Liquids and gases can fl ow because molecules can fl ow, move past one another.

A gas can be compressed easily, whereas a liquid can also be compressed but with greater degree of effort.

I. 1. Thickness of 10 coins: 7 cm, 70 mm

2. Thickness of one coin: 0.7 cm or 7 mm

3. Thickness of 100 coins: 70 cm , 700 mm

Answers to WorksheetsWORKSHEET 1

1. a. Force

b. Friction

c. Lesser

d. Nails and screws

e. Reduce

2. a. Fluid friction

b. Newton

c. Kinetic friction

d. Streamlining

e. Static friction

3. a. False b. True

c. False d. True

4. a. Force can change the state of rest and state of motion of a body. For example, a stationary ball is kicked. A moving cycle comes to a stop on application of brakes.

b. Friction can be reduced by the use of lubricants and by the use of ball bearings.

WORKSHEET 2

1. a. opposes

b. grooves, ridges

2929

c. brittle

d. Fishes, birds

2. a. False b. False

c. True d. False

3. a. iv b. iii c. i d. ii

4. a. Sliding friction: When a body begins to slide over a surface, the force exerted by the surface on the object is called sliding friction. It is equal to the force required to keep the object in motion.

Sliding friction is less than static friction.

Rolling friction: When an object rolls over a surface, the force which opposes the rolling motion of the object is

called rolling friction. Rolling friction is less than sliding friction.

b. Static Friction: The maximum opposing force between the object and the surface in contact with it, so long as the object remains stationary even on applying an external force, is called static friction.

If we push an object and it does not move. Even on increasing the force the object does not move. When the force increases, the friction between two surfaces becomes maximum, and the object still remains stationary. A slight increase in force can now overcome static friction and the object begins to move.

3030

Total marks: 50Time: 3 hours

Model Test Paper 1

Section AA. Fill in the blanks: [5]

1. The molecules of a substance are in a state of ________________ motion.

2. A ________________ has a defi nite shape that is not easy to change.

3. ________________ is a measure of the distance between two points.

4. For precise and accurate measurement of mass of an object, an ________________ is used.

5. Friction opposes ________________ of an abject.

B. Multiple choice questions: [5]

1. The smallest particle of an element which is indivisible, is

a. molecule b. element c. atom d. nucleus

2. SI unit of mass is

a. gram b. quintal c. newton d. kg

3. The stem of a laboratory thermometer has markings from

a. 0 °C to 100 °C b. –10 °C to 100 °C

c. –10 °C to 110 °C d. 0 °C to 110 °C

4. Wet roads become slippery due to

a. decreasing friction b. increasing friction c. slippery shoes d. None of these

5. Sweeping the fl oor using a broom is an example of a

a. Push b. Pull c. change in direction d. None of these

C. State True or False: [5]

1. A balloon rising up in air does not experience friction.

2. The Fahrenheit scale has 180 divisions.

3. The time 10:15 in a 24-hour clock would mean quarter to ten in the morning.

4. A metre rule is used to measure the length of a curved line.

5. SI unit of force is Newton.

D. Name the following: [4]

1. Highly compressible state of matter.

2. A gas used in the kitchen.

3. A balance used in the science laboratory.

4. A push or a pull acting on an object.

3131

Section BA. Defi ne the following: [3]

1. A molecule

2. Physical quantities

3. Time

B. Short answer questions: [12]

1. What is area? Write its formulae.

2. Why are lubricants needed in machines?

3. Give the difference between:

a. Static friction and rolling friction

b. Beam balance and physical balance

C. Long answer questions: [12]

1. Explain with examples how you can use force as a push, pull and change of direction.

2. From among the given pictures, state which among them have maximum friction, and which has the least friction.

3. Observe the given picture and answer the following questions:

a. What state of matter is inside the tyre?

b. State the specifi c property of this state of matter due to which it can be contained in a small space. Why?

c. Can you explain any other property of this state?

D. Numerical: [4]

a. The area of a square plot of land is 900 m2. Find the length of its side.

b. Convert into the given units:

i. 1500 gm = ___________ kg ii. 1 hectare = ___________ m2

3232

Learning Objectives

Students will be able to: defi ne simple machines and its types.

understand types of levers

calculate and understand mechanical advantage

defi ne and understand inclined plane, screw, wedge, wheel and axle, and pulley

learn about the maintenance of machines

4 Energy

Warm-upAsk students about objects in use at home which make their work easy.

They will come up with answers such as scissors, nails, knives, hammer, sewing machine, fi re tong, hand pump to draw out water, a pulley to lift a bucket full of water from a well and a whole lot of appliances they use at home.

Read the Warm Up section from the book.

Use it to explain the topic simple machines.

Concept ExplanationSimple machines, Types of simple machines• Discuss with the students that the objects

mentioned above are simple machines. Such machines help us to perform tasks with ease and effi ciency.

• Emphasise the fact that a sewing machine and a cycle are not simple machines but complex machines.

• Read the related sections from the book.

• Machines and their functions are explained to the students.

• Make the students understand about the types of simple machines.

• To reinforce ask the students to do the related Pause and Do section from the book.

• Ask the students to answer the related questions from the Part II of the Exercises.

Lever, Mechanical advantage• Ask them to tell the difference between a

knife and a hammer, a scissor and a shear for cutting metal.


• Defi ne the terms fulcrum, load and effort. Use these to explain to them about class-one, class-two and class-three levers.

• Explain to them the mechanical advantage of three types of levers.

• Use examples given in the textbook to make the students understand how to calculate mechanical advantage of different levers.

3333

• To reinforce, ask the students to do the related Pause and Do section from the book.


Inclined plane, Screw, Wedge, • Read the related sections from the book.

• Defi ne a slide is called an inclined plane.

• Discuss with the students about the advantage of inclined planes in real life.

• Ask students to tell the difference between a screw and a nail.

• Defi ne that a screw is a simple machine with grooves cut around it. The grooves are called the threads of the screw. It can be driven into a rigid object more easily than a nail.

• To prove that a screw is an inclined plane ask them to do the activity given in the related section.

• Explain to them that one or two inclined planes join together form a wedge. Wedges are used as separating or holding devices.

• To reinforce, ask students to do the related Pause and Do section from the book.


Wheel and axle, Pulley, Maintenance of machines • Read the related sections from the book.

• Defi ne wheel and axle and explain to them that a steering wheel, a screw driver and a drilling machine are all examples of the wheel and axle arrangement.

• Defi ne pulley to the students.

• Ask them to tell the difference between a single fi xed pulley and a movable pulley.

• Discuss the points on the maintenance of machines.


Reinforce• To reinforce, read the Summary and

Glossary sections from the book.

• Use Part I of the Exercises to conduct a quiz contest in the class.

Explore • To explore, ask the students to do the

Learning Zone section from the book.

3434

Worksheet 1

1. Choose the correct answer and fi ll in the blanks.

a. A plier is an example of ________________ (class I, class III) lever.

b. The effi ciency of any machine is determined by its ________________

(velocity ratio, mechanical advantage).

c. Class II levers are used as ________________ (speed multipliers, force multipliers).

d. Nut and bolt is an example of a ________________ (wedge, screw).


a. A screw jack is a simple machine used to raise heavy objects off ________ the ground.

b. In a single fi xed pulley, the effort required to lift a load is half the load. ________

c. In class III levers, the effort arm is longer than the load arm. ________

d. A sewing machine is a simple machine. ________

3. Match the following.

a. Pulley i. Class II lever

b. Wheel barrow ii. Class I lever

c. Knife iii. Simple machine

d. Claw hammer iv Class III leve


a. What is a wedge? Give two examples.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

b. The mechanical advantage of a machine is 3.5. How much effort is required to lift a load of 28 N?

_____________________________________________________________________

_____________________________________________________________________

3535

Worksheet 2

1 Fill in the blanks.

a. A steering wheel is an example of _____________ arrangement.

b. A _____________ is a device that makes our work easy.

c. When a machine is being used, _____________ is being transferred from one point to another.

d. _____________ for cutting metals have long handles and short blades.

2. Name the following:

a. Type of lever which has the effort arm shorter than the ________________load arm.

b. In this type of pulley, the axle is free to move. ________________

c. A flat sloping surface, with one end higher than the other. ________________

d. A type of lever in which the load is located between the ________________effort and the fulcrum.


a. How can you increase the mechanical advantage of a lever?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

b. Give reason. Machines should be regularly oiled.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

c. A fi re tongs has a length of 12 cm and the distance of the effort from the fulcrum is 3 cm. Calculate its mechanical advantage.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

3636


PART 1

A. 1. (a) a lever 2. (a) a lever

3. (a) split a log 4. (b) fulcrum

5. (b) two 6. (c) screw driver

7. (a) pulley

B. Choose the correct option and fi ll in the blanks.

1. effort 2. screw 3. pulley

4. nut cracker 5. inclined plane

6. fulcrum 7. class two levers

C. Write T for true and F for false.

1. False 2. True 3. False

4. False 5. True 6. True

7. False 8. True 9. False

10. False

D. Name the simple machine.

1. pulley 2. scissors 3. pulley

4. inclined plane 5. Class III lever

PART 2

A. 1. A pulley, inclined plane, screw.

2. It makes our work easier by applying less effort more work can be done.

3. The object that has to be moved, lifted or cut.

4. Scissors, pliers.

5. Nut and bolt, cork screw.

6. Inclined plane

7. Splitting wood, carving and chiseling.

8. Screw driver.

9. Inclined plane or pulley.

B. Short answer questions.

1. It is a simple device with a few or no moving parts. It makes our work easier.

2. It is the ratio of load to effort. More the mechanical advantage, more effi cient is the machine.

3. A machine makes our work easier by changing the direction of the force applied. A bucket full of water is heavy when lifted up, but using a pulley it can be easily lifted.

4.

Screw

5. A lever helps us to lift and move something with less effort.

6. Load x Load Arm = Effort x Effort Arm.

7. The axis around which a pulley rotates is fi xed. In this pulley, the force required to lift a body is equal to its weight.

C. Long answer questions.

1. A lever is a rigid rod that can move freely around a fi xed point of support.

Nut cracker (Class-two lever)FE

L

2. An inclined plane is a simple machine because it can lift up heavy objects with ease by using a gradual sloping surface.

For example, It is used to carry luggage at railway stations.

It is used in hospitals to wheel up patients.

3737

3. Mechanical advantage of a lever can be increased by increasing the length of the effort arm.

4. Machine should be kept clean and free from dust.

If a machine is made of iron, it should be painted.

To reduce friction, a machine should be regularly oiled.

5. A wedge is a modifi cation of an inclined plane. One or two inclined planes, join together to form a wedge.

They are used as separating or holding devices.

For example, nut and bolt and screw jack.

6.

Movablepulley

Fixed pulley

Load

A

B

A combinati on of movable and fi xed pulleys

Fixed pulley: The axis around which a pulley rotates is fi xed. In this pulley, the force required to lift a body is equal to its weight. The distance moved by the effort is equal to the distance moved by the load.

Movable pulley:The effort required to lift a load is half the load, as the load is shared equally by two parts of the rope supporting the pulley. A movable pulley is used along with a fi xed pulley to change the direction of effort in a convenient direction.

D. Numericals:

1. MA= L/E Ans. = 10 N.

2. MA =L/E Ans. = 10

3. MA = Effort arm/ Load arm

Ans. = 2.5


Ans. = 0.5


Ans. = 3

E. Explain the following terms:

1. Simple machines: It is a simple device with a few or no moving parts, it makes our work easier. We can overcome a large force by applying less effort.

2. Complex machines: Complex machines are made of two or more simple machines. Some examples are a sewing machine, a car, a scooter.

3. Inclined plane: An inclined plane is a simple machine that can lift up heavy objects with ease by the use of a gradually sloping surface.

For example, it is used to carry luggage and cross a bridge at railway stations.

It is used in hospitals to wheel up patients.

4. Wedge: A wedge is a modifi cation of an inclined plane. One or two inclined planes, join together to form a wedge.They are used as separating or holding devices.

For example, nut and bolt and screw jack.

5. Class one lever: The fulcrum is in between the load and effort. It can have a mechanical advantage equal to, less than or greater than one. Class one levers always changes the direction of force. For example, scissors, pliers, see-saw, etc.

F. Give reasons:

1. To lift a heavy load directly upwards is diffi cult, but using an inclined plane it can be pushed up quite easily. Sloping surfaces are quite useful in hospitals to wheel up patients or railway stations to carry luggage by passengers and coolies.

2. Oiling of machines increases their life. There will be no wear and tear of machines due to friction.

3. If parts of machines are made of iron, exposure to moisture can cause rusting. This will decrease the effi ciency of a

3838

machine. Hence machines should be varnished or painted.

4. Class three levers have the effort in between the load and fulcrum. Hence their MA is less than 1.But the advantage of such levers is that the distance moved by the load is greater than the distance moved by the effort. Hence it is a speed multiplier.

G. Differentiate between the following:

1. Class II lever: The load being in the middle, effort arm of a class II lever is longer than the load arm. Hence class II levers are used as force multipliers. They are more effi cient machines.

Class III levers have the effort in between the load and fulcrum. Hence their MA is less than 1. But the advantage of such levers is that the distance moved by the load is greater than the distance moved by the effort. Hence it is a speed multiplier.

2. Simple machines: It is a simple device with a few or no moving parts, it makes our work easier. We can overcome a large force by applying less effort.

Complex machines: Complex machines are made of two or more simple machines. Some examples are a sewing machine, a car, a scooter.

3. Wedge: A wedge is a modifi cation of an inclined plane. One or two inclined planes, join together to form a wedge.They are used as separating or holding devices.

For example, axe, chisel, nail, etc.

Inclined plane: An inclined plane is a simple machine that can lift up heavy objects with ease by the use of a gradually sloping surface.

For example, It is used to carry luggage or to cross the bridge at a railway station.

It is also used in hospitals to wheel up patients.

LEARNING ZONE


1. Do it yourself.

2. a. Third class lever

b. less than 1

c. simple machine

d. No

e.

3.

(a) (b) (c)

LL

LEEF F

F

W

4. A→load; B→fulcrum;

C→effort; D→load arm;

E→effort arm

Think and Answer

1. A seesaw is a simple machine. This machine has balancing loads on either end with a fulcrum in the middle. Therefore, the other end will immediately fall down and touch the ground and the effort becomes zero.

2. While we are going down the hill, speed of the cycle increases due to gravity so we must be very careful.

3. We can use simple machine as crow bar to move the rock from the road.

4. It is easy to lift a bucket of water from a well using a pulley because pulley changes the direction of the effort in a convenient direction.

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WORKSHEET 1

1. a. Class I

b. Mechanical advantage

c. Force multiplier

d. Screw

2. a. True b. False

c. False d. False

3. a. iii b. i c. iv d. ii

4. a. Wedge: A wedge is a modifi cation of an inclined plane. One or two inclined planes, join together to form a wedge. They are used as separating or holding devices. For example, an axe and a nail.

b. MA = L / E [2]

3.5 = 28 / E

E = 28 / 3.5

E = 8 N

WORKSHEET 2

1. a. wheel and axle

b. machine

c. effort

d. Shears or pliers

2. a. Class III

b. Movable

c. Inclined plane

d. Class II

3. a. Mechanical advantage can be increased by keeping the load between the effort and the fulcrum, so that the effort arm is always longer than the load arm.

b. To prevent wear and tear of machines and reduce friction between the moving parts of a machine, it should be oiled regularly.

c. MA = Effort arm / load arm

MA = 3 / 12 = 0.25

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Learning Objectives

Students will be able to: defi ne light and sources of light

differentiate between luminous and non-luminous objects

recognise bio-luminescence in objects

differentiate and recognise transparent, opaque and translucent objects

understand about rectilinear propagation of light and speed of light

defi ne shadow, its characteristics and shadows formed by a point source of light and extended source of light

explain the working of a pinhole camera

defi ne eclipse, solar eclipse, lunar eclipse, and their types

5 Light

Warm-upRead the Warm-up section from the book.

Ask students to give answer to the questions given in this section. Use this to explain the term light and is sources.

Concept ExplanationLight, Sources of light (luminous, non-luminous and bio-luminescence objects Defi ne that light is a form of energy which excites the sensation of vision.

Ask students to tell examples of some natural and artifi cial sources of light.

Ask students to tell examples of some natural and artifi cial sources of light.


Ask students to tell examples of some luminous, non-luminous, bio-luminescence objects.

To reinforce, ask them to do the related activity given in this section.


Transparent, Translucent and Opaque objectsRead the related sections from the book.

Ask students to tell examples of some transparent, translucent and opaque objects.

To reinforce ask them to do the related activity and Pause and Do section.


Rectilinear propagation of light, ShadowRead the related sections from the book.

Defi ne that the light travels in a straight line in a medium which is called the rectilinear propagation of light.

4141

To reinforce, demonstrate the related experiment given in this section.

Ask the students to do the related activity given in this section.

Defi ne shadow and do the related activity to explain how to form shadow.

Discuss characteristics of shadow with the class. Also, explain how shadow is cast by a point source of light and extended source of light.

Explain the working of a pinhole camera to the class and also demonstrate the related experiment to the students.

To reinforce, ask the students to do the related Pause and Do section from the book.

Ask the students to answer the related questions from the Part II of the Exercise.

Eclipse, Lunar eclipse, Solar eclipseRead the related sections from the book.

Defi ne an eclipse takes place when one heavenly body, such as the moon or a planet,

moves into the shadow of another heavenly body.

To reinforce demonstrate the related experiment given in this section.

Use the blackboard to explain the position of earth, moon and sun when lunar and solar eclipses occur.

Explain the various types of solar eclipses to the class.




ExploreTo explore, ask the students to do the Learning Zone section from the book.

4242

Worksheet 1

1 Fill in the blanks.

a. Light does not pass through ________________ objects.

b. Light travels in a straight line with a speed of ________________m/s.

c. A ________________ eclipse occurs when the moon blocks the sun completely.

d. Butter paper is a ________________ medium.

2. State true or false.

a. Candle is a luminous object. _________

b. Light takes a path that takes the longest time. _________

c. A penumbra is a region of complete darkness. _________

d. It is safe to look at a lunar eclipse. _________


a. An illuminating object. _______________

b. The property of light to travel in a straight line. _______________

c. A collection of several rays moving in an organised manner. _______________

d. An image that can be obtained on a screen. _______________


a. What is a solar eclipse? Name any two types of solar eclipses.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

b. What are the characteristics of an image formed by a pinhole camera?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

4343

Worksheet 2


a. A fi refl y is a

i. luminous organism ii. illuminating organism

iii. bio-luminescent organism iv. All of these

b. When the rays of light start from a point and travel in various directions, then it is called a

i. convergent beam ii. parallel beam

iii. divergent beam iv. None of these

c. A penumbra is formed by a

i. overhead street lights ii. extended source of light

iii. an electric bulb. iv. All of these

d. The image formed by a pinhole camera is

i. inverted ii. virtual

iii. erect iv. on the same side as the object

2. Answer the questions:

a. Give the difference between a convergent and divergent beam with the help of a diagram.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

b. What is bioluminescence? Name two bioluminescent organisms.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

4444


PART 1

A. 1. (b) 2. (b) 3. (c) 4. (a)

5. (b) 6. (d)

B. 1. luminous 2. transparent

3. rectilinear propagation of light

4. energy 5. rectilinear propagation

6. luminous, illuminating

C. 1. False 2. True 3. True

4. True 5. False 6. True

7. True

D. a. iv b. ii c. v

d. iii e. i

PART 2

A. 1. Most objects around us are non- luminous.

2. Luminous 3. No.

4. A solar eclipse occurs on a new moon day.

5. Yes 6. Light cannot bend.

7. Sun 8. The object is translucent.

9. No. 10. Yes.

B. 1. Natural sources: Sun and stars

Artifi cial sources: Candles and electric bulbs

2. Most objects around us do not give out light themselves, but become visible when light from a luminous body falls on them and then enters into our eyes.

3. Rectilinear propagation of light means light travels in a straight line.

4. Certain objects through which we cannot see clearly because they scatter or diffuse the refracted light. For example, butter paper, frosted glass, etc.

5. Image formed by a pinhole camera is

(a) inverted

(b) real image, since it can be formed on a screen.

(c) such as the size of the image can be diminished or enlarged.

6. A solar eclipse can occur only when the moon passes between the earth and the sun. If the moon’s shadow happens to fall on the earth’s surface, people living in that area are not able to see the sun.

C. 1. Take three rectangular pieces of cardboard of the same size. Make tiny holes in each cardboard at the same height from the base. Place them on a table in such a way that each cardboard is exactly behind the other with the holes in a straight line. Place a candle in front of the fi rst cardboard in such a way that the fl ame is exactly in line with the candle fl ame. You can see the candle fl ame from the last hole. Now displace the cardboard in the middle slightly.

You will notice that the fl ame is not visible.

Thus, as long as the holes in the cardboard are aligned in a straight line with the candle fl ame, you can see the light.

This proves light travels in a straight line or rectilinear propagation of light.

2. Properties of a shadow:

It is always black in colour regardless of the colour of the object.

It only gives the shape of the object.

Shadows are always formed on the opposite side of the source of fl ight.

3. A simple pinhole camera is based on rectilinear propagation of light. It consists of a light proof box with a tiny hole on one side. As the light falls on the pinhole, it forms an inverted image of the object on the opposite side of the box. The smaller the size of the pinhole the sharper the image formed.

4. Solar eclipse: When the moon orbits the earth, it moves between the sun and the

4545

earth. At a certain position, the moon blocks the light of the sun reaching the earth. This causes a solar eclipse. The moon casts a shadow on the earth.

SUN MOON EARTH

Umbra

Penumbra

Solar eclipse

Lunar eclipse: When the earth orbits the sun, there comes a time when the earth comes between the sun and the moon. The shadow of the earth falls on the moon, due to which people living on that side of the earth are not able to see the moon for some time. This is an eclipse of the moon, i.e., lunar eclipse.

UmbraUmbra

EARTHSUN MOON

Penumbra

Lunar eclipse

D. Explain the following:

1. Total solar eclipse: A total solar eclipse takes place when the view of the sun is completely blocked by the moon. The part of the earth that falls under the umbra region has a total solar eclipse. The sky becomes very dark.

2. Partial lunar eclipse: A partial lunar eclipse occurs when the moon is in the penumbra region of the earth. The moon receives some light of the sun that it refl ects to the earth. Hence the moon is partially visible to people living on that side of the earth.

3. Shadow: When light falls on an opaque object it forms a shadow on the opposite side away from the source of light. The area of darkness formed by an object

obstructing light is called a shadow.

4. Umbra: The shadow cast by a point source is sharp and dark. This region of complete darkness is called Umbra.

5. Penumbra: When an electric bulb is placed in front of an opaque object, a shadow is formed, the inner circular portion of which is dark and well defi ned. This is called Umbra. There is a circular ring around the umbra which is a a faint shadow. This region of partial darkness is called penumbra.

E. Differentiate between the following:

1. Luminous objects: Bodies that give out light of their own are called luminous bodies. For example, the sun and the stars.

Non luminous objects: Most of the objects around us do not give light themselves but become visible when light from a luminous body falls on them and then enters into our eyes. Such bodies are called non-luminous.

For example, table, trees, books, etc.

2. Ray and beam: A ray of light is a single path along which light travels. It is represented by a line with an arrowhead drawn to show the direction of propagation of light.

Beam: A beam of light is broader and a collection of several parallel rays moving in an organised manner. A torch gives a beam of light.

3. Solar eclipse: When the moon orbits the earth, it moves between the sun and the earth. At a certain position, the moon blocks the light of the sun from reaching the earth. This causes a solar eclipse. The moon casts a shadow on the earth.

Lunar eclipse: When the earth orbits the sun, there comes a time when the earth comes between the sun and the moon. The shadow of the ear falls on the moon, due to which people living on that side of the earth are not able to see moon for some time. This is an eclipse of the moon or lunar eclipse.

4646

4. Translucent objects: There are certain objects through which we cannot see clearly. The light that passes through these objects is diffused or scattered. Such objects are called translucent objects. For example, tracing paper, ground glass.

Opaque objects: Objects such as wood, stone, metals sheets, paper, etc. do not allow light to pass through them so they form shadows. Such objects are called opaque objects.

Learning ZonePicture Based Questions

1. Do it yourself.

2.

3. (a) A → lunar eclipse; B → solar eclipse

(b) (i) moon (ii) earth

(c) When sun, moon and earth are in a same line and earth is in between the sun and the moon.

(d) When sun, moon and earth are in a same line and moon is in between the earth and the sun.

4. Do it yourself.

Think and Answer1. Since light falls from the different sources

and directions on the players. Thus, there forms multiple shadows of the players on the ground.

2. Do it yourself.

3. Take an opaque sheet of paper. Put some oil on it. After some time you will observe that the opaque sheet of paper has been converted into a translucent sheet.

4. At noon the sun is at the top of our head while in the morning and in the evening the sun islow in the horizon. Thus, the shadow at noon is the shortest and in the morning and in the evening the shadows are longest.


WORKSHEET 1

1 a. opaque b. 3 x 108 m/s

c. solar d. translucent

2. a. True b. False

c. False d. True

3. a. Moon

b. Rectilinear propagation of light

c. Beam d. Real

4. a. Solar eclipse: When the moon orbits the earth, it moves between the sun and the earth. At a certain position, the moon blocks the light of the sun

to reach the earth. This causes a solar eclipse. The moon casts a shadow on the earth.

Partial solar eclipse and Annular solar eclipse.

b. Characteristic of image formed by a pinhole camera is as follows:

i. Inverted

ii. Real image, since it can be formed on a screen.

iii. The size of the image can be diminished or enlarged.

4747

WORKSHEET 2

1. a. iii. Bioluminescent

b. iii. Divergent

c. iv. All of these

d. i Inverted

2. a.

Parallel beam

Divergent beam

Convergent beam

Beams of light

When the rays of light start from a point and travel in various directions, then the collection of such rays is called a divergent beam of light.

When the rays of light coming from different directions meet at a point, then a collectionof such rays is called a convergent beam of light.

b. A bioluminescent organism produces light which is the energy released from [2] chemical reactions occurring inside the organism.The chemical energy gets converted into light energy. For example, a fi refl y, some kinds of bacteria and even sharks.

4848

Learning Objectives

Students will be able to: explain magnets, discovery of magnets, shapes of magnets

differentiate between magnetic and non-magnetic materials

learn about the properties of magnets

learn the concept of magnetic fi eld and magnetic fi led of the Earth

learn different methods to make a magnet

differentiate between permanent and temporary magnets

understand about the storage and handling of magnets and their uses

6 Magnetism

Warm-upRead the warm up section from the book.

Ask students about objects in use at home or outside which carry magnets.

Concept ExplanationMagnets, Discovery of magnets, Shapes of magnets, Magnetic and non-magnetic materialsDiscuss with the students that the an object which attracts or repulses another object is called magnet.


Discuss about the magnetic force and magnetic materials.

Ask some questions based on the topic discovery of magnets to the students.

Ask them to observe the shapes of some artifi cial magnets.

Ask them to do the activity given in this section to differentiate between magnetic and non-magnetic materials

To reinforce ask the students to do the related Pause and Do section from the book.


Properties of magnetsRead the related section from the book.

Use the experiments given in this section to make them understand the properties in a better way

To reinforce, ask the students to do the related Pause and Do section from the book.


Magnetic fi eld, Magnetic fi eld of the earth, Making of a magnet, Permanent and Temporary magnetsRead the related sections from the book.

Explain that the the space around a magnet where magnetic force is experienced is called magnetic fi eld.

4949

Use the experiments and activities given in these sections to make them understand these concepts in a better way.



Storage and handling of magnets, Uses of magnets Read the related sections from the book.

Discuss the terms magnetisation, demagnetisation and self-demagnetisation.

Make them understand how to store and handle magnets to prevent demagnetisation and self-demagnetisation.

Ask the questions based on the uses of magnets in real life to the students.





ExploreTo explore, ask the students to do the Learning Zone section from the book.

5050

Worksheet 1


a. It is a naturally occurring magnet.

i. Magnetite ii. Horseshoe magnet

iii. Lodestone iv. Alnico magnet

b. Magnetism is maximum at the

i. centre of a magnet ii. poles

iii. outside a magnet iii. None of these

c. It is a sure test of magnetism.

i. Attraction ii. Repulsion iii. Induction iv All of these


a. A magnet can lose its magnetism by rough handling. _________

b. Magnets can be stored for a long time without any loss in _________ magnetism.

c. Lodestone is an ore of iron called magnetite. _________

d. The south pole of the earth’s magnet points towards the _________ earth’s geographic south pole.


a. What are magnetic lines of force? Illustrate with a diagram.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

b. Give the difference between temporary and permanent magnets.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

5151

Worksheet 2


a. A ferromagnetic substance ________________

b. Sailors use it to fi nd direction. ________________

c. Magnets that retain their magnetism for a short period of time. ________________

d. A U-shaped magnet used in an electric bell. ________________


a. Magnetic poles can exist single. _________

b. Magnetism is permanent whe the method of induction is used. _________

c. Magnets can be stored at room temperature. _________

d. A freely suspended magnet rests in the North-South direction _________

3. Match the following.

a. Natural magnet i. Magnet made of soft iron

b. Artifi cial magnet ii. Electromagnet

c. Very powerful magnet iii. Ring and disc shaped magnets

d. Temporary magnet iv. Lodestone


a. How are magnets used in Maglev trains?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

b. Why does a freely suspended magnet point in the north south direction?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

5252


PART 1

A. 1. (c) 2. (b) 3. (d) 4. (b)

5. (a) 6. (c) 7. (d) 8. (c)

9. (a)

B. 1. magnetic 2. north-south 3. poles

4. repel, attract 5. compass 6. pairs

7. earth

C. Write T for true and F for false:

1. False 2. False 3. True

4. True 5. False 6. True

7. False 8. True

D. Name the following:

1. Lodestone

2. Iron and nickel

3. Magnetic compass

4. Magnetic lines of force

5. Repulsion

6. Electromagnet

7. Electromagnet

8. Demagnetisation.

PART 2

A. 1. A material that has the property of attracting objects made of certain substances like iron, cobalt and nickel is called a magnet.

2. Iron and nickel

3. The magnetic force is concentrated at two regions, called the poles of a magnet.

4. Magnets which do not lose their magnetic property even when the cause producing the magnetism is removed are called permanent magnets.

Magnets which lose their magnetic property when the cause producing the magnetism is removed are called temporary magnets.

5. No, because attraction is maximum at the poles of a magnet.

6. Yes, magnetic poles exist in pairs.

7. Opposite poles of a magnet attract each other.

B. 1. Magnets were discovered when a shepherd living in Greece, Magnesia noticed that the ferrule of his stick and the nails in his sandals got stuck to a magnetic rock. The stone was named magnetite also known as lodestone.

2. Naturally occurring magnets such as lodestone are weak and are not available in any particular shape.

Artifi cial magnets are strong and can be made into any shape.

3. Magnets should be kept at room temperature using a magnetic keeper.

4. A freely suspended magnet comes to rest in the north south direction.

5. By using a magnet, iron fi lings can be separated from sand.

6. Defi ne:

(a) Magnet: A material that has the property of attracting objects made of certain substances like iron, cobalt and nickel is called a magnet.

(b) Magnetism: The property of a magnet to attract iron and nickel is called magnetism.

(c) Poles of a magnet: The magnetic force is concentrated at two regions on either side of a magnet, called the poles of a magnet.

(d) Self-demagnetization: When a magnet is left unused for a long period of time, it gradually loses its magnetism.

7. Write two examples for each:

(a) Magnetic material: Iron and Cobalt

(b) Non-magnetic material: Plastic and aluminium

5353

8. Give reasons for the following:

(a) The opposite poles of a pair of magnets are placed beside each other separated by a bar of ferromagnetic material . This ensures that the magnetic alignment is not disturbed.

(b) When magnets are rubbed against each other, the regular arrangement of molecular magnets is disturbed and they lose their magnetism.

9. Properties of a magnet:

(a) Magnets attract magnetic material

(b) Magnetic poles exist in pairs.

(c) A freely suspended bar magnet comes to rest in North- South direction.

(d) Like poles repel and unlike poles attract.

C. 1. To prove like poles of a magnet repel and unlike poles of a magnet attract each other: Freely suspend a bar magnet. It will come to rest in North- South direction.

Bring the north pole of another bar magnet close to the north pole of the hanging magnet. There will occur repulsion between them.

Next turn the side and bring the south pole of a bar magnet close to the north pole of the hanging bar magnet. There will occur attraction between them.

2. Hang a bar magnet freely and rotate it. It will come to rest in a particular direction.

Rotate it again, it will again point in the same direction. Use a magnetic compass to prove that the magnet rests in the North- South direction.

3. A magnetic compass consists of a magnetised steel needle horizontally mounted on a pivot, which is able to move freely. The north pole of a magnetic compass will always point towards the geographic north.

4. If a magnet is repeatedly hammered, dropped from a height, heated or left unused for a long period of time it loses its

magnetism. Thus the regular arrangement of molecular magnets is disturbed and the magnet is demagnetised.

5. Uses of magnets:

(i) They are used to construct motors and generators.

(ii) They are used in electric bells.

(iii) They are used to sort out magnetic and non-magnetic substances from scrap.

(iv) They are used in cranes.

6. An iron bar can be made into a magnet by rubbing it continuously with a bar magnet from one end to the other end at least 30 to 40 times. The magnet produced by this method is temporary magnet.

7. Care of magnets:

Magnets should always be kept at room temperature away from moisture. The best way of storing a magnet is by the use of a magnetic keeper. This ensures magnetic alignment is not disturbed. A bar magnet makes use of two magnetic keepers whereas a horseshoe magnet uses only one keeper.

D. 1. A horse shoe magnet: A horse shoe magnet is a U- shaped permanent magnet that produces a strong magnetic fi eld. Both its poles point in the same direction.

2. Magnetic poles: The magnetic force is concentrated at two regions on either side of a magnet called the poles of a magnet.

3. Electromagnet: An electromagnet is a temporary magnet that works as long as electric current passes through it. When the current is switched off the magnetism is lost.

4. Magnetic fi eld: The space around a magnet till where magnetic force is experienced is called magnetic fi eld.

E. Differentiate between:

1. Magnets which do not lose their magnetic property even when the cause producing the magnetism is removed are called permanent magnets.

5454


2. Naturally occurring magnets such as lodestone are weak and are not available in any particular shape.

Artifi cial magnets are strong and can be made into any shape.

3. The materials that are attracted towards a magnet are called magnetic materials or ferromagnetic materials. For example, iron, nickel, cobalt and steel.

Materials that are not attracted by a magnet are called non-magnetic materials.

For example, zinc, copper, plastic, wood, etc.

4. There is attraction between unlike poles of a magnet. There is repulsion between like poles of a magnet.

5. In single touch method, an iron bar is rubbed with a magnet repeatedly from one end to the other end without lifting it.

In double touch method two bar magnets of equal strength are rubbed from the centre of the iron bar towards either end with their opposite poles moving away from each other.

6. The earth’s geographic north pole is actually the south pole of the earth’s magnet.

The north pole of a bar magnet is always attracted to the earth’s magnetic south

pole. That is why the north pole of our bar magnet always points towards the geographic north pole of the earth.

F. Separate magnetic and non-magnetic materials:

Magnetic: nail, safety pin, hair clip

Non-magnetic: Tooth pick, coin, gold bangle, plastic cap, elastic band, pencil, crayons, paper, matchstick.

Learning ZonePicture Based Questions

1. (b)

2. Magnet A > Magnet B > Magnet C

3. Do it yourself.

Think and AnswerThe metal will not be magnetised properly while rubbing is done haphazardly in nature.

1. It might lead to discontinuities in the material.

2. Yes, the poles of horse shoe magnets attract each other.

3. Although a pencil sharpener’s body is made up of plastic but the blade used to sharpen the pencil is made up of iron or some other magnetic material, so the sharpener gets attracted to the magnet.

4. Drop the magnet from heights or hit the ground by the magnet number of times. We will observe after some time that the magnet will be demagnetize partially or permanently.

Answers to Assessment 2A. 1. (c) 2. (a) 3. (b) 4. (d)

5. (c)

B. 1. Movable Pulley:The effort required to lift a load is half the load, as the load is shared equally by two parts of the rope supporting the pulley. A movable pulley is used along with a fi xed pulley to change the direction of effort in a convenient direction.

2. Mechanical Advantage: It is the ratio of the load to the effort. MA will determine how effi cient a machine will be.

3. Solar eclipse: A solar eclipse can occur only when the moon passes between the Earth and the Sun. If the moons shadow happens to fall on the Earth’s surface, people living in that area are not able to see the Sun.

5555

4. Electromagnet: An electromagnet is a temporary magnet whose magnetic property is due to the fl ow of electric current around a soft iron bar.

5. Magnetic fi eld: The space around a magnet till where magnetic effect is felt is called a magnetic fi eld.

C. 1. (d) 2. (e) 3. (b)

4. (a) 5. (c)

D. 1. Mechanical advantage

2. Machine

3. Hybrid solar eclipse

4. Partial solar eclipse

5. Lodestone

E. 1. Class II lever: The load being in the middle, effort arm of a class II lever is longer than the load arm. Hence, class II levers are used as force multipliers. They are more effi cient machines.

Class III levers: They have the effort in between the load and fulcrum. Hence their MA is less than 1.But the advantage of such levers is that the distance moved by the load is greater than the distance moved by the effort. Hence it is a speed multiplier.

2. Solar eclipse: When the moon orbits the Earth, it moves between the Sun and the Earth. At a certain position, the moon blocks the light of the sun from reaching the Earth. This causes a solar eclipse. The moon casts a shadow on the Earth.

Lunar eclipse: When the Earth orbits the Sun, there comes a time when the earth comes between the Sun and the moon. The shadow of the Earth falls on the moon, due to which people living on that side of the Earth are not able to see moon for some time. This is an eclipse of the moon called Lunar eclipse.

3. Geographic North Pole: The south pole of the earth’s magnet points towards the geographic north pole of the earth. It is actually the north pole of the earth.

Magnetic North Pole: The magnetic north pole of the earth lies towards its geographic south pole.

4. Temporary magnet: An electromagnet is a temporary magnet which is made by passing electric current through a soft iron bar. The poles of a temporary magnet can be reversed. The strength of temporary magnets can be increased considerably.

Permanent magnet: It is made of steel. The poles of permanent magnets are fi xed.Its strength cannot be increased.

F. 1. F 2. T 3. T 4. T 5. F

G. 1. MA has no unit because it is a ratio of two physical quantities that have the same unit which canceled to each other.

2. Levers, pulleys, wedge, inclined plane, screw, wheel and axle.

3. Some objects do not produce light, but they shine by refl ecting the light from other objects. Such objects are called illuminated objects.

4. An electromagnet is a temporary magnet because it works as a magnet only when electric current is passed through it. The poles of such a magnet can be reversed. It can be switched on and off at will.

5. Magnets are used in cranes. They are used to construct electric motors and generators.

H. 1. An electromagnet is a temporary magnet which is made by passing electric current through it. A coil of wire is wound around a soft iron bar and an electric current is passed through it.

2. A simple pinhole camera is based on rectilinear propagation of light. It consists of a light proof box with a tiny hole on one side. As the light falls on the pinhole, it forms an inverted image of the object on the opposite side of the box. The smaller the size of the pinhole the sharper the image formed.

Image formed by a pinhole camera is,

a. is inverted

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b. is real image, since it can be formed on a screen.

c. and the size of the image can be diminished or enlarged.

3. Inclined plane: An inclined plane is a simple machine that can lift up heavy objects with ease by the use of a gradually sloping surface.

For example, It is used to carry luggage or to cross the bridge at a railway station.

Also, it is used in hospitals to wheel up patients.

Screw: A screw is a modifi cation of an inclined plane. It has grooves cut around it. The grooves are called threads of the screw. It can be driven into a rigid object more easily than a nail.

Screw is used to join pieces of wood, metal sheets, handles of pans, etc.

4. Load arm = 100cm

Effort arm = 60 cm

M.A = Effort armLoad arm = 60

100 = 0.6

5. Solar eclipse: When the moon orbits the Earth, it moves between the Sun and the Earth. At a certain position, the moon blocks the light of the Sun from reaching the Earth. This causes a solar eclipse. The moon casts a shadow on the Earth. Solar eclipse can be Total, Annular and Partial.

Lunar eclipse: When the Earth orbits the Sun, there comes a time when the earth comes between the Sun and the moon. The shadow of the Earth falls on the moon, due to which people living on that side of the Earth are not able to see moon for some time. This is an eclipse of the moon called Lunar eclipse.

I. 1. Picture C has all three magnetic materials.

2. Picture A has no magnetic material.

3. Picture B has only 1 magnetic material.

Answers to WorksheetsWORKSHEET 1

1. a. iii b. ii c. i

2. a. True b. False

c. True d. False

3. a. The space around a magnet where magnetism is felt is called magnetic lines of force. They run from North to South and are closed , continuous curves. They never intersect each other.

b. Magnets which do not lose their magnetic property even when the cause producing the magnetism is removed are called permanent magnets. Magnets made of steel and alnico magnets are permanent magnets.


Magnets made of soft iron and electromagnets are temporary magnets

WORKSHEET 2

1. a. Nickel or iron

b. Magnetic compass

c. Temporary magnet

d. Horseshoe magnet

2. a. False b. False c. True d. True

3. a. iv. b. iii. c. ii. d. i.

4. a. Maglev trains are the fastest in the world. Superconducting magnets are used at the bottom of the train and on the tracks on which the train fl oats. These trains move due to the repulsion between magnets.

b. A freely suspended magnet points in the North-South direction, because the earth has its magnetic south pole towards the geographic north pole. That is why our magnet is attracted to the earth’s magnetic south pole which is actually the geographic north pole.

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Total marks: 50Time: 3 hours

Model Test Paper 2

Section AA. Fill in the blanks: [5]

1. ______________ were invented to perform activities with ease and effi ciently.

2. A ______________ is a modifi cation of an inclined plane.

3. The ______________ is the main source of light on the Earth.

4. ______________ travels in a straight line.

5. ______________ ______________ always occur in pairs.

B. Multiple choice questions: [5]

1. A pair of scissors is an example of a/an

a. wheel and axle b. lever c. pulley e. inclined plane

2. They are used as force multipliers

a. Class I levers b. Class II levers c. Class III levers d. All of these

3. Objects which do not allow light to pass through them are called

a. Transparent b. Translucent c. Opaque d. None of these

4. A freely suspended magnet always rests in the

a. South – North direction b. North – South direction

c. East – West direction d. No particular direction

5. A very powerful magnet used in cranes is a/an

a. permanent magnet b. horse shoe magnet

c. electromagnet d. natural magnet

C. State True or False: [5]

1. Egyptian sailors used the magnetic compass.

2. Steel can be magnetised

3. The image formed by a pinhole camera is always virtual.

4. Shadows are always formed on the opposite side of the source of light.

5. Tracing paper and frosted glass are transparent objects.

D. Circle the odd one out: [5]

1. Copper, silver, nickel, bronze, aluminium

2. Water, air, glass, butter paper

3. Scissors, mango cutter, pliers, beam balance, see-saw

4. Sun, stars, moon, candles, electric lamp

5. Heating, hammering, magnetic keeper, high temperature

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Section BA. Defi ne the following: [2]

1. Class I lever

2. Umbra

B. Short answer questions: [12]

1. Write the characteristics of the image formed by a pinhole camera.

2. How should we store bar magnets?

3. Give the difference between:

a. Inclined plane, and wheel and axle

b. Temporary and permanent magnets

C. Long answer questions: [16]

1. Draw diagrams of a fi xed pulley and a movable pulley. What is the advantage of using a fi xed pulley?

2. How can you convert an iron bar into a magnet? Explain this method through an activity. Will this magnet be temporary or permanent?

3. Picture based question.

Figure-1 Figure-2

Look at the picture and answer the following questions:

a. What type of shadow is formed by the fi rst picture?

b. How does the shadow change in the second picture?

c. At what position of the football from the screen two shadows are formed?

d. Name the shadows.

4. In each of the pictures shown above mark the position of the Load, Effort and Fulcrum and state the class of lever.

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Answers to Model Test Paper 1

Section A

A 1. random 2. solid 3. Length

4. electronic balance 5. speed

B 1. c 2. d 3. c 4. a 5. a


4. False 5. True

D 1. gas 2. LPG 3. physical balance

4. Force

Section B

A 1. Matter is composed of very tiny particles called molecules.

2. Something that can be measured.

3. Interval between two events is time.

B 1. The amount of surface covered by a closed shape.

Area of a square = side × side;

Area of a rectangle = length × breadth × height;

Area of a triangle = (1/2) × base × height;

Area of a circle = r²

2. To reduce friction in machines.

3. a. Static friction: The maximum value of frictional force between two surfaces which can prevent one surface from sliding over the other.

Rolling friction: The friction that occurs when one object rolls across the other.

b. Beam Balance: It consists of a straight beam of wood (or metal) of length

about 50 cm. The beam has a support just at its middle, having a pointer. Two identical pans are suspended at the two ends of the beam by means of strings of equal length. Each pan is at the same horizontal distance from the support, i.e., the length of the beam of each pan from the support is equal. The balance can be held up by the support.

Physical Balance: A physical balance is a modified and highly sensitive version of the beam balance. It is used in science laboratories for the accurate measurement of chemicals.

C. 1. Pushing a door to close it and pulling a rope by two teams during a tug of war game. The direction in which an object is pulled or pushed is called the direction of force. A player kicks a moving football to make it move in another direction while playing. The kick is the force he applies to change the direction of the motion of the football.

2. Maximum friction: Pushing box without wheel by a man

Minimum friction: Ball bearings

3. a. gas

b. A gas can be easily compressed. Its volume can be compressed to several times its original volume. This is because the distance between the molecules of a gas is very large.

c. A gas can fl ow because its molecules can move past one another.

D a. 30 m b. i. 1.5 kg ii. 10,000 m²

Answers to Model Test Paper 2

Section A

A 1. Machines

2. screw

3. Sun

4. Light

5. Magnetic poles

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B 1. b 2. b 3. c 4. b. 5. c


4. True 5. False

D 1. nickel

2. butter paper

3. beam balance

4. magnetic keeper

Section B

A 1. If the fulcrum is anywhere between the load and the eff ort, the lever is a class-one lever. Examples of such levers are a pair of scissors, pliers, see-saw, crowbar, handle of a water pump, claw-hammer, etc.

2. The region of total darkness is called umbra.

B 1. The real and inverted image is formed on the screen.

If the hole is made quite wide, each point on the object will produce a large patch on the screen. These patches will overlap and the fi nal image will get blurred. The smaller the hole, the sharper will be the image. However, if the hole is made very narrow (less than 0.1 mm), very little light will pass through it and the image formed will be faint. The image remains sharp when the distance between the screen and the pinhole is increased. If the pinhole camera is moved nearer the object, the image on the screen will become large.

2. It can be stored at room temperature using magnetic keepers.

3. a. Inclined plane: A fl at sloping surface, with one end higher than the other.

Wheel and axle: An arrangement in which a larger wheel rotates around a smaller rod called an axle.

b. Permanent magnets: those magnets that retain magnetism for a very long period of time.

Temporary magnets: magnets that retain magnetism only for a short period of time.

C. 1.

Fixed pulley

Fixed pulley

Load

Movablepulley

Fixed pulley

Load

A

B

A combination of movable and fi xed pulleys

In case of a movable pulley, we fi nd that the eff ort required to lift a load is half the load, as the load is shared equally by the two parts of the rope supporting the pulley.

2. Rub an iron bar with a magnet repeatedly. To magnetise an iron bar AB using a bar magnet, place one of the poles of a bar magnet, say the north pole, over one end of the iron bar, say end A. Without lifting the bar magnet, move it along the length of the iron bar, stroking it till you reach the other end, B, of the bar. On reaching end B of the iron bar, lift the bar magnet and bring the same north pole to point A of the iron bar, and then move the magnet from point A to point B again. The process needs to be repeated about 30 to 40 times. This process is called magnetisation of the iron bar by the single-touch method.

3. Do it yorself.

4. Do it yourself.

6 the physics science orbit - saraswati house material... · 2018-07-03 · the physics kishwar...

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