ncert science textbook for class 8th chapters 1 to...

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NCERT Science Textbook for Class 8th Chapters 1 to 16 2016 © 10x10learning.com, Page 1 PART ONE FOR CAPABILITY BUILDING OF TEACHERS This section for teachers is merely an attempt to bridge the ‘facility availability divide’ that exists in many part of India. It is well known that all Teachers do not have equal access to a good library for preparing good quality teaching content. Bridging this divide is the only intent here. The objective is to inform the students to the extent possible. CONTENT The Textbook already gives Keywords and Summary of main aspects at the end of each chapter under ‘What You Have Learnt’. These are very good for revision and help in understanding the main points. Therefore, these are to be studied from the Book and are not repeated here. This document only gives some additional material as may further help in clarifying the subject matter. Essay type questions are answered here to serve as a cross-check for student’s own answers. Do not try to learn these by heart, but to understand and link the concepts to what has already been studied in Class 7 th . Also see power point presentation on Introduction to Science. This Section begins by listing the 18 chapters in this Science Book, as pertaining to living matter’ or non-living matter’. The third column indicates the subject area for that chapter, to be studied in higher classes. Nos. of the Chap ter Title of the Chapter Specialized subject area of the chapter Later on to be studies in advance study of Other remarks/ Higher studies subject matter or professional skills LIVING MATTER

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Page 1: NCERT Science Textbook for Class 8th Chapters 1 to 1610x10learning.com/wp-content/uploads/2016/05/Scienc… ·  · 2016-07-14NCERT Science Textbook for Class 8th 2016 Chapters 1

NCERT Science Textbook for Class 8th

Chapters 1 to 16

2016

© 10x10learning.com, Page 1

PART ONE FOR CAPABILITY BUILDING OF TEACHERS

This section for teachers is merely an attempt to bridge the ‘facility

availability divide’ that exists in many part of India. It is well known that all

Teachers do not have equal access to a good library for preparing good quality

teaching content. Bridging this divide is the only intent here. The objective is to

inform the students to the extent possible.

CONTENT

The Textbook already gives Keywords and Summary of main aspects at

the end of each chapter under ‘What You Have Learnt’. These are very good

for revision and help in understanding the main points. Therefore, these are

to be studied from the Book and are not repeated here.

This document only gives some additional material as may further help in

clarifying the subject matter. Essay type questions are answered here to serve

as a cross-check for student’s own answers. Do not try to learn these by

heart, but to understand and link the concepts to what has already been

studied in Class 7th

. Also see power point presentation on Introduction to

Science.

This Section begins by listing the 18 chapters in this Science Book, as

pertaining to ‘living matter’ or ‘non-living matter’. The third column

indicates the subject area for that chapter, to be studied in higher classes.

Nos.

of

the

Chap

ter

Title of the Chapter Specialized

subject area of

the chapter

Later on

to be

studies in

advance

study of

Other

remarks/

Higher

studies

subject matter

or

professional

skills

LIVING MATTER

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NCERT Science Textbook for Class 8th

Chapters 1 to 16

2016

© 10x10learning.com, Page 2

RELATED

1. 2. 3

1 Crop Production and

Management

Plant life Botany

and

Agricultur

al

Sciences

Agricultural

Sciences

7 Conservation of Plants

and Animals

Eco-system Botany

and

Zoology

Environment

al Studies

8 Cell – Structure and

Functions

Basis of all

life- Plant,

Animal and

Human

Botany,

Biology,

Zoology

Bio-

chemistry

Studied by

humans for

creation of

new materials

such as

Plastics and

Synthetic

fibres

9 Reproduction in

Animals

Animal / Bird

life

Zoology Zoology

10 Reaching the Age of

Adolescence

Human

anatomy and

physiology

Biology All Medicinal

studies

18 Pollution of Air and

Water

Eco-systems,

environment

and geography

Environm

ental

studies,

Geograph

y

And

environmenta

l studies

NON-LIVING

MATTER RELATED

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NCERT Science Textbook for Class 8th

Chapters 1 to 16

2016

© 10x10learning.com, Page 3

3 Synthetic Fibres and

Plastics

Chemistry Inorganic

Chemistry

Inorganic

Chemistry,

Chemical

engineering

6 Combustion and Flame Energy Physics Physics and

Environment

al Science

4 Materials: Metals and

Non-Metals

Geography Geograph

y

Geography

and Mining

Engineering

5 Coal and Petroleum Geography Mineralog

y

Mining

Engineering

11 Force and Pressure Mechanics Physics Mechanical

Engineering

12 Friction Mechanics Physics Mechanical

engineering

14 Chemical Effects of

Electric Current

Physics and

Chemistry

Electricity

and Power

Electronics,

Electrical

Energy,

Advanced

Studies in

Matter and

Energy

15 Some Natural

Phenomena

Geography Geograph

y

Geography

and

Hydrology,

Meteorology

13 Sound Sound energy Physics Physics,

Astronomy

and Radiant

Energy

16 Light Physics Physics Physics,

Astronomy

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NCERT Science Textbook for Class 8th

Chapters 1 to 16

2016

© 10x10learning.com, Page 4

CHAPTER 1 Crop Production and Management

INTRODUCTORY

1. The modern systems of irrigation, for the purpose of agriculture, were

developed about 200 years ago. Historically, agriculture has been

dependent upon manual work and seasonal rains. Traditional systems of

irrigation were all dependent on rain. As rainfall depends on climatic

conditions and cannot be controlled by humans, agricultural activity had

high uncertainty.

2. Along with this Chapter, please see Chapter 4 of NCERT Textbook in

Geography for Class 8th

. Geography Chapter 4 tells about the different

Farm Systems and Crops cultivated in different countries today. The

Crop Production in India is on a much smaller size farm than the crop

production in the USA. This is partly due to the difference in the soil,

climate, expanse of plain land available and the technology used in these

two regions of the world. The difference is also due to historical

development of the two societies and their different social and economic

structures.

and Radiant

Energy

17 Stars and the Solar

System

Our Universe

and Astronomy

Astronom

y

Astronomy

and Quantum

Mechanics

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NCERT Science Textbook for Class 8th

Chapters 1 to 16

2016

© 10x10learning.com, Page 5

QUESTIONS

3. Q1. Fill in the blanks:

a) The same kind of plants grown and cultivated on a large scale

at a place is called crop.

b) The first step before growing crops is preparation of the soil.

c) Damaged seeds would float on the top.

d) For growing a crop, sufficient sunlight , water and nutrients

from the soil are essential

4. Match A with correct answer in B in the following:

a) Kharif crop (e) paddy and maize

b) Rabi crop (d) wheat, gram, pea

c) Chemical fertilizers (b) Urea and super phosphate

d) Organic manure (c ) Animal excreta, cow dung, urine, plant

waste.

5. Q3 Give two examples each of (a) Kharif crop and (b) Rabi crop

a) Kharif crops: Paddy, maize, soyabean, groundnut and cotton are a

few of the Kharif crop that are grown in the rainy season from June

to September each year

b) Rabi crop: Wheat, mustard, gram, peas, and linseed are examples

of Rabi crop that are grown in winter from October to March each

year

6. Q 4 Write one paragraph each in your own words on the following:

a) Preparation of soil is the first activity in the process of growing any

crop whether a kharif crop or a rabi crop. During preparation, the

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Chapters 1 to 16

2016

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soil is ploughed to turn and loosen it. The loosening of the soil allows

the roots of the crop plants to reach deep down the soil. It also helps

to trap air between the soil particles. The roots use this air for

breathing. The loose and turned soil also helps earthworms and other

organisms to grow. Earthworms are ‘friends’ of plants as the tiny

burrowing in soil helps to trap more air between the soil particles for

the roots to breathe. As soil contains minerals, water, air and humus,

preparation of soil helps in mixing these up properly. It also brings up

the more nutrient rich soil from the bottom layers to the top. (116

words)

b) Sowing is the second activity in growing of a crop. For this, clean

and healthy, good quality seeds are selected. These are then soaked in

water for a few hours or overnight. The next morning these are filled

in a funnel like tool that allows only one or two seeds to pass through

it at a time. This is important because some space is needed between

two plants. A seed drill is also used for the purpose. In this way

sowing of seeds is completed without causing wastage or damage to

the seeds. (93 words)

Picture of Sowing activity

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Chapters 1 to 16

2016

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c) Weeding is an important part of growing of a crop. Weeds are the

unwanted plants that grow on their own because their roots or seeds

are already spread in the soil. The separation and removal of weeds

from the crop plants is called weeding. The weeds are harmful to the

crop plants because they use up the nutrients that should in fact be

used by the crop plants. Some weeds are poisonous and therefore,

harmful both to humans and animals. So when the crop plants are still

small, the weeds are to be identified and uprooted by hand or with the

help of a tool called ‘khurpi’. They are then removed from the field

and disposed off at a distance or burnt after drying them in a separate

place. Certain chemicals called ‘weedicides’ are also used to control

weeds in place of manual weeding. These chemicals are dissolved in

water and sprayed. They destroy the weeds without harming the crop

plants.

(Note: (c) also covers Q 9 on what are weeds and how can they be

controlled?)

d) Threshing is the activity of separating the grain seed from the chaff

that covers it. The crop is first harvested, either by cutting the plant

stalk just above the ground, manually with a sickle, or

automatically by a harvester machine. The cut out plants are then

beaten softly, to rub off the outermost covering of the grain called the

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2016

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‘chaff’. Then through winnowing the grain is separated from the

chaff.

Winnowing is mostly done by hand by women. A rectangular

base with raised borders along its three sides, is made of straw and is

very light. This tool, in Hindi, is called the ‘soop’. About one

kilogram of grain covered with chaff, is lifted up in the soop by

holding its two sides and raising it to above the head level. From there

the grain is and poured down on to the ground. The wind blows away

the light chaff, allowing the heavier grain to collect as a heap.

7. Q 5 Explain how fertilizers are different from manure

Fertilizers are chemical substances that are rich in certain nutrients

needed by the crop plants. These are produced in factories with the help

of machines. Urea, Super phosphate, Ammonium sulphate, and

potassium are examples of fertilizers. They help to give a higher yield

from a crop but they also make the soil less fertile. They have also

become a major source of water pollution.

Manure is the natural decomposed mixture of cow-dung, dead plants

and humus. Traditionally only manure was used in agriculture. Mixing

of manure with the soil increases the capacity of the soil to retain water.

It makes the soil more porous and due to this more air is trapped in the

soil. Manure also increases the friendly microbes in the soil and

improves the soil texture.

8. Q6 What is irrigation? Describe two methods of irrigation that conserve

water.

The supply of water to the crop plants at different intervals is called

irrigation. Water is necessary for agriculture because 90 per cent of

the content of all plants is water. Irrigation is the activity through which

water is supplied to the crop plants. Irrigation is needed for the sprouting

of the seeds, for proper development of the plants, flowers and fruits.

Nutrients from the soil get dissolved in water and reach the plants. To

retain the moisture in the soil the fields have to be irrigated regularly.

Wells, tube-wells, ponds, lakes, rivers, dams, canals are sources of water

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Chapters 1 to 16

2016

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for irrigation. Drip system and Sprinkler system are two methods of

irrigation that conserve water. Under the Drip System water falls drop

by drop very near the roots and therefore water is not wasted at all. In

the Sprinkler system pipes with nozzles at regular intervals are used. As

the water passes through the pipes the nozzles rotate to sprinkle the

water as if during the rainfall. This system also conserves water and is

very useful for uneven land and sandy soil.

9. Q 7 If wheat is sown in the kharif season what would happen?

The wheat crop needs less water and a long sunshine season for

maturing. If wheat is sown in kharif months of June to September, the

rains would destroy the crop. Therefore, wheat is sown as a rabi crop in

October after the end of the rainy season, to prevent it from getting

destroyed before harvest.

10. Q 8. Explain how soil gets affected by the continuous plantation of crops

in a field

11. Q 9. What are weeds? How can we control them?

Please see answer to Question No. 4 (d) above for this question.

12. Q. 10 Arrange the following boxes in proper order to make a flow chart

of sugarcane crop production.

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2016

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13. Crossword: Down

a) Irrigation

b) Storage

c) Crop

Across

d) Harvester

e) Gram

f) Winnowing

CHAPTER 2. MICRO-ORGANISM

Questions 1 to 4 can easily be done by the student by reading the Chapter two

or three times.

1. Ploughing the field

2. Preparation of soil

3.Sowing

4.Manuring5. Irrigation6.Harvesting

7. Sending crop to sugar

factory

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2016

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Q5 What are the major groups of micro-organisms?

Answer. Micro-organisms or microbes are classified into four major groups.

These are called (1) bacteria (single cell) (2) fungi ( multi-cell)(3) protozoa

(single cell) and (4) algae (single and multi-cell). These four groups have the

common characteristic of growing externally on all living matter. In addition

there is a fifth group called viruses but a virus can only grow inside another

living cell. It cannot grow externally like the four major groups.

Q6 Name the micro-organisms which can fix atmospheric nitrogen in the

soil?

Answer. Certain bacteria and blue-green-algae can fix atmospheric nitrogen

into the soil by converting it in to useable compounds.

Q7 Write ten lines on the usefulness of micro-organisms in our lives.

Answer. Micro-organisms are very useful in our lives as they help in

breaking down and converting more complex substances in to compounds that

are more easily used by plant, animals and human. In our daily lives curds,

bread, cheese and pickle are made with the help of useful and human-friendly

micro-organisms. In industry, the micro-organism called ‘yeast’ is used on a

large scale to produce alcohol, wine and vinegar by converting sugar in to

alcohol. Several medicines, such as antibiotics are also produced with the help

of microorganisms on a commercial scale. Antibiotics made from fungi and

algae are also mixed in the feed given to livestock to prevent infection. They are

also used to prevent many plant diseases. In this way we find that micro-

organisms are useful in our lives.

Q8. Write a short paragraph on the harms caused by micro-organisms.

Answer. Microorganisms can also cause harm. Several micro-organisms

called ‘pathogens’ cause many plant, animal, and human diseases. Other micro-

organisms spoil food articles because convert the nutrient in to toxic or

poisonous substance. Spoilt food emits a different smell, develops a different

colour and is also bad to taste. These changes are due to growth of fungus that

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Chapters 1 to 16

2016

© 10x10learning.com, Page 12

make the food toxic. Consuming of such spoilt food can result in food poisoning

and diseases. Another harmful effect is that medicines made from

microorganisms should be used strictly with in the date of expiry. After the date

of expiry the microorganisms stop being useful in sickness and become harmful.

Q9. What are antibiotics? What precautions must be taken while using

Antibiotics?

Answer. Antibiotics are special medicines produced commercially with the

help of microorganisms such as bacteria and fungi. They can cure several

diseases. But antibiotics should be used strictly before the date of expiry

indicated on the medicine. After the date of expiry the microorganism base in

the medicine becomes harmful and will result in causing poisoning instead of

curing the disease.

CHAPTER 3 SYNTHETIC FIBRES AND PLASTICS

Q. 1 Explain why some fibres are called synthetic.

Ans. Some fibres are made from chemicals by man. They are not made from

natural primary products such as cotton and jute. Therefore, in contrast to

natural fibres these man-made fibres are called ‘synthetic fibres’. The word

‘synthetic’ means artificial because it is ‘synthesized together or blended

together through a chemical /mechanical procedure’ by human beings. It is

opposite of ‘natural’

Q. 4 Give examples which indicate that nylon fibres are very strong

Ans Nylon fibres are used for making parachutes, ropes for mountain

climbing, ropes for hauling of heavy luggage in ships and shipyards, tents for

camping in forests and for the army, car seat belts, socks for winter and cold

regions only because it is a very warm fibre, bags for army that need to be tough

under all conditions, sleeping bags for travel as they can be rolled in to a small

space, very light curtains, umbrellas.

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Chapters 1 to 16

2016

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Nylon thread is prepared from coal water and air. It is tested to be stronger

than steel thread. It is also very long-lasting and does not wear out easily.

Therefore, many articles used by the soldiers in war are prepared from nylon.

However, nylon is highly combustible, meaning that it catches fire very quickly.

Q.5 Explain why plastic containers are favoured for storing food

Plastic containers are very lighter and lower priced than metal

containers, are unbreakable, give a clean look and are easy to handle. In

addition they are non reactive do not get affected by rust or bacteria and do not

corrode like the metals.

Q6 Explain the difference between thermoplastic and thermosetting plastics

Thermoplastics get deformed and loose their original shape easily if

kept in places with high temperature or when heated. This is because they

conduct heat. Therefore, they cannot be used for making cooking utensils.

Thermosetting plastics, such as bakelite and melamine, are poor conductors of

heat and resist fire. Therefore, they are used for making handles of cooking

utensils such as pressure cookers, kitchenware, electric switches and plugs,

plug-points, and also floor tiles that do not wear out easily.

Q 7 Explain why the following are made of thermosetting plastics:

(a) Saucepan handles

Saucepans are used for cooking over fire. Its handle is made from

thermosetting plastics as such plastics can tolerate heat better than other

plastics. They are also a poor conductor of heat and therefore, the handle does

not get warm or hot while cooking.

(b) Electric plugs / switches / plug boards

Electric plugs / switches / plug boards are made from thermo-setting plastics

because these are points in the electric system that are touched by human beings

to switch on or switch off the current. To prevent damage through electric shock

these articles need to be made of material that is a poor conductor of heat and

electricity. Thermo-setting plastics are very poor conductors of heat and electric

current. As such they are used for making electric plugs and switches and any

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Chapters 1 to 16

2016

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part of the electricity flow system that comes in to contact with the human hand.

Also thermosetting plastics are very long lasting.

Q8 Categorize the materials of the following products into ‘can be recycled’

and ‘cannot be re-cycled’

Telephone instruments, plastic toys, cooker handles, carry bags, ball point

pens, plastic bowls, plastic covering on electrical wires, plastic chairs, electric

switches.

Can be recycled - because are made

of thermoplastics

Cannot be re-cycled -because are

made of thermosetting plastic

Plastic toys, carry bags, ball point

pens, plastic bowls, plastic chairs

Cooker handles, telephone

instruments, electric switches,

covering on electrical wires

Q9 Rana wants to buy shirts for summer. Should he buy cotton shirts or

shirts made from synthetic material? Advice Rana, giving your reason.

Rana should be advised to buy a cotton shirt for summer because it will

keep him cooler than a synthetic material shirt. This is because cotton shirt

weave has space between each fibre when it is woven into a fabric. The fibre of

a synthetic cloth is very tightly woven leaving no space for air to flow through

the cloth. This makes synthetic clothes warmer than cotton clothes. Therefore,

in summer cotton shirt is better while in winter a synthetic shirt is better. The

tighter weave of synthetic cloth is also the reason why it takes longer than

cotton to get soaked in water.

Q 10 Give examples to show that plastics are non-corrosive in nature.

In electric switches, plugs and plug points, we see that the outer frame that

is made of thermosetting plastics does not get effected by air, water, or heat.

Therefore these do not wear and tear easily. However, the metal screw with

which the switch is fixed of the metal parts of a plug are seen to get corroded or

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2016

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rusted. Often they need to be replaced after a year or so. This is because the

metallic part is corrosive while the thermosetting plastic part is non-corrosive.

Q11 Should the handle and bristles of a tooth brush be made of the same

material? Explain your answer.

No. The bristles are made from thermoplastic that is more flexible and

therefore makes brushing of teeth possible without damaging the gums. The

handle of the tooth brush is made of a harder version of thermoplastic as it

needs to remain firm to grip while brushing, and also needs to hold the bristles

together for a longer period of use. Therefore, the handle and the bristles of a

tooth brush cannot be made of the same material.

Q 12. ‘Avoid plastics as far as possible’. Comment on this advice.

Plastics are non-bio-degradable and they continue to exist in garbage

for more than 500 years without decaying. For this reason they are a major

source of pollution. If they are burnt they emit (give off) poisonous fumes that

pollute the air.

As such plastics are a source of both environment pollution as well as air

pollution. Therefore, in our daily lives we should avoid plastics as far as

possible. Moreover, when cows and other animals eat garbage they eat up parts

of plastic and plastic bags also. The plastic bags do not get digested and cover

the lining of the animal’s stomach. This is known to cause their untimely death.

Therefore, plastic bags should not only be avoided, but they should not be

thrown around. Use of bio degradable bags needs to be encouraged.

In sum, the reasons that plastics cause air pollution, environmental pollution,

and are not bio-degradable they should be avoided as far as possible.

Q13 Match the terms in column A correctly with phrases in column B

1. Polyester - fabrics do not wrinkle easily

2. Teflon - used to make non-stick cookware

3. Rayon - prepared by using wood pulp

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2016

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4. Nylon - used for making parachutes and stockings

Q 14 ‘Manufacturing syntheticfibres is actually helping conservation of

forests’. Comment

This is not a correct statement. Forests do not give an natural

fibre. Cotton and jute are the only two natural fibres and both are

cultivated. Jute grows almost naturally in the delta regions of rivers and

not in the forests. So forests in not way are conserved due to synthetic

fibres. In fact rayon is the only synthetic fibre that is made by treating

wood pulp artificially to make it stronger. So manufacturing of rayon

uses up a lot of wood from the forests, and cannot be said to be

conserving forests. If synthetic fibres are burnt they emit poisonous

gases that cause air pollution. For this reason also they can be said to

be harmful to forests. In sum, synthetic fibres cannot be said to be

conserving forests in any manner. The given statement is false and

misleading.

Q15 Describe an activity to show that thermoplastic is a poor conductor of

electricity.

Take a plastic bucket and fill it two third with water. Place an

‘immersion rod’* in to the water and connect it to the plug point. Switch

on the immersion rod.

Immediately, observe that small bubbles of water form along the

immersion rod as it starts to get heated. After 15 minutes it is

observed that water in the bucket is very warm and small fumes of

steam are forming on the surface. However, when the outside of the

plastic bucket is touched by hand no shock from the flow of electric

current is felt. This shows that the bucket made of thermoplastic is a

poor conductor of electricity. However, if the immersion rod is

allowed to remain ‘on’ for a longer period, the outside of the bucket

will also become slightly warm to touch. This shows that

thermoplastics are a poor conductor of electricity but they do

conduct some heat.

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2016

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In case a metal bucket is used for warming water with an

immersion rod, the bucket will get as heated as the water and the

chances of getting a shock from the flow of current will be very

high. For this reason it is advisable to use an immersion rod with a

plastic bucket only. Also because thermoplastic is a poor conductor

of electricity, electric gyser is also made of thermoplastic or

thermosetting plastic.

*An Immersion rod is a simple electrical household appliance. It is

the cheapest device for warming water for bathing during winters as

it consumes very little electricity. It is available for about Rs 120/- to

Rs 150/- from any electrical goods shop and can be used for several

years.

CHAPTER 4 MATERIALS - METALS AND NON-METALS

In this Chapter the chemical equation and formulae are introduced. For this

the basis are the following formulae and valancy:

Radical Formula Valancy

Sulphate SO4 2

Sulphite SO3 2

Nitrate NO3 1

Nitrite NO2 1

Carbonate CO3 2

Phosphate PO4 3

Hydroxide OH 1

As you study the reactions and write the word equations the above table will

be very useful. For example in Question 9 and wherever sulphate / sulphuric

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acid is involved the word equation will have SO4. Similarly for others in the list

The details of the formula for three acids is given below: (In the equations (=)

sign is used in place of ‘arrow’ sign in the book)

1) Sulphuric acid H2SO4 = 2H+ + SO4

-

2) Nitric acid HNO3 = H+ + NO3

3) Hydrochloric acid HCl = H+ + Cl

In the case of sulphuric acid the sulphate radical has a valency of 2. This means

that two hydrogen atoms are required to complete the stability of the equation.

Therefore H2 SO4. Displacement is also due to gaining or losing of ions by the

atoms.

Certain oxides and alkalis can neutralize acids. Bases include such oxides as

well as hydro-oxides

a)Caustic soda (sodium hydroxide) NaOH = Na + OH

b)Caustic potash (potassium hydroxide) KOH = K + OH

c)Slaked lime ( calcium hydroxide) Ca(OH)2 = Ca ++

+ 2OH

Basic oxides are always oxides of metals. Acidic oxides are compounds of

non-metals and oxygen with react with bases to form salts. An example is

Carbon dioxide gas (CO2) which reacts with sodium hydroxide (NaOH) to form

the salt sodium carbonate:

CO2 + 2NaOH = Na2CO3 + H2O

When an acid is neutralized by a base a salt is formed. An example is the

formation of the common salt or sodium chloride (NaCl) from sodium

hydroxide and hydrochloric acid = NaOH + HCl = NaCl+H2O. We know that

H2O is water.

FROM THE CHAPTER

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Q6. Give reason for the following:

(a) Aluminum foils are used to wrap food items.

Aluminum foils are used to wrap food items because aluminum is a

metal and because of the characteristic of ‘malleability’. It can be beaten in to

thin sheets called foils. The foil retains the heat longer due to which the food

remains warm for a longer period. In addition the foil prevents air from

reacting with the wrapped food. This keeps it fresh for long. The foil is also

light and odourless. This makes it an ideal wrapping for food items.

(b) Immersion rods for heating liquids are made up of metallic

substances.

Metallic substances can be beaten into any shape. They are also very good

conductors of heat and electricity. Therefore, household appliances such as

Immersion rods that can warm water for bathing during winter are made of

metallic substances.

(c) Copper cannot displace zinc from its salt solution

Zinc is more reactive than copper. Therefore copper cannot displace

zinc from zinc sulphate. The rule is that a more reactive metal can replace a

less reactive metal, but a less reactive metal cannot replace a more reactive

one. For this reason, zinc can displace copper from copper sulphate.

(d) Sodium and potassium are stored in kerosene.

Sodium is a metal and is very reactive to oxygen in the air. As oxygen

is present in water, sodium reacts vigorously with water also. For this reason

sodium starts creating a lot of heat during its reaction with oxygen both in air

and in water. Therefore, it is stored in kerosene.

Potassium is also a very soft metal that can be cut with a knife. It is very

reactive to oxygen both in air and water. Therefore, potassium also is stored in

kerosene

Q7 Can you store lemon pickle in an aluminum utensil? Explain.

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Lemon is sour because its nature is acidic. Aluminum is a metal. All metals

react with acids because their oxides are basic by nature. Therefore, lemon

pickle cannot be stored in an aluminum utensil.

Q 9. What happens when -

(a) Dilute sulphuric acid is poured on a copper plate?

When dilute sulphuric acid is poured on a copper plate, copper sulphate

is formed. This is written in equation as copper (Cu) + sulphuric acid (SO4) =

Copper sulphate CuSO4

(b) Iron nails are placed in copper sulphate solution.

Write word equation of the reaction involved.

When iron nails (Fe) are placed in copper sulphate (CuSO4) solution the

colour of the solution changes from blue to green due to formation of a new

substance called ‘iron sulphate’. The word equation for this reaction is Copper

sulphate solution (blue) + Iron (Fe) sulphate solution (green) + copper deposit

on iron nails (brown deposit)

Q 10 Saloni took a piece of burning charcoal and collected the gas in a test

tube.

(a) How will she find the nature of the gas?

She will pour some limewater in to the test tube. The gas collected will

turn the limewater milky. This will indicate that the gas collected is carbon-

dioxide. When the limewater turns milky Calcium carbonate is formed

(b) Write down word equations of all the reactions taking place in this

process.

Charcoal + Oxygen (O) = Carbon-dioxide (CO2) + lime water Ca OH2 =

Calcium carbonate (CaCO2) + Water (H2O).

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Q11 What is the reason for the loss in weight of old jewellery that has been

polished?

When old jewellery is polished the gold rust that had accumulated over it is

scrubbed off along with a very tiny part of the gold surface. This gives the

jewellery a new shine but also results in loss of weight.

COMPARATIVE TABLE OF ACID / BASE / METALS / NON METALS

FOR REVISION AND EASIER UNDERSTANDING

Acids (sour) Bases (bitter and

soapy)

Metals Non-metals

Nature is acidic Nature is basic All metals are

malleable, ductile and

sonorous. Malleability

means they have the

quality of being beaten

in to thin sheets and

cast into various

shapes. Ductile means

that they can be drawn

in to wires. Sonorous

means that when hit

they emit balanced

sound waves that cause

a ringing or a echo like

sound. For this reason

bells are made of

metal.

Non metals

are not

malleable, or

ductile or

sonorous.

All metals are very

good conductors of

heat and electricity.

Therefore, all electric

wires are made of

Non-metals

are not good

conductors of

heat or

electricity

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various metals or

alloys of metals.

Alloys are new metals

created by mixing two

or more natural metals.

Many alloys are better

for making certain

kinds of machines

because they have the

good qualities of more

than one metal.

Some metals such as

sodium and potassium

react very vigorously

with oxygen in water

and air. Both are

therefore stored in

kerosene.

Others metals, such as

iron, react very slowly.

But all metals react

with water. They

become corrosive

(weak in strength and

worn out) due to this

reaction.

Generally,

non-metals

do not react

with oxygen

in the water,

but they do

react to

oxygen in the

air.

Phosphorous

is a very

intensively

reactive non-

metal that

catches fire if

exposed to

air. To

prevent this

reaction,

phosphorous

is stored in

water.

All Metals react with Generally

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acids and produce

hydrogen gas that

burns with a ‘pop’

sound when a match is

brought near the test

tube. However, Copper

does not react with

hydrochloric acid even

after heating, but it

does react with

sulphuric acid.

non-metals

do not react

with acids

Metals react with

Bases such as sodium

hydroxide to produce

hydrogen gas.

Non-metals

react with

bases in a

complex

manner.

In an aqueous solution

one metal displaces

another metal from its

compound. This is

called ‘displacement

reaction’

The general rule for

this displacement is

that a more reactive

metal will replace the

less reactive metal, but

a less reactive metal

cannot replace a more

reactive metal. For this

reason Zinc which is

more reactive will

replace Copper, but

Non-metals

do not show

any such

displacement

reaction

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Copper which is less

reactive will not

replace Zinc.

Acid are sour to

taste

Bases are bitter to

taste and soapy to

touch)

Metals are generally

hard. Exceptions are

sodium and potassium

that can be cut with a

knife.

Non-metals

are generally

brittle and

turn into

powder easily

Citric acid is

found in citric

fruits such as

oranges and

lemons

Bases in nature

occur as Calcium

hydroxide in Lime

water (choona

pani – used for

white-washing the

walls)

Mercury is the only

metal that exists as a

liquid at room

temperature.

All other metals are

solids at room

temperature. They need

to be heated to

different heat level to

reach their melting

point. Only in their

molten form the metals

can be cast in to shapes

Ascorbic acid

(Vitamin C) in

Amla and citrus

fruits

Sodium hydroxide

/ potassium

hydroxide in soap

All metals are reactive

to air and water. Some

like sodium and

potassium are so

intensely reactive to

oxygen both in air and

water, that they need to

be stored in kerosene.

Tartaric acid in

tamarind, grapes

and raw mango

Magnesium

hydroxide in milk

of magnesia

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Lactic acid in

curds

Oxalic acid in

spinach or palak

Litmus is a natural

indicator made

from lichen that

grow on the floor

of the oceans. It

has a mauve

(purple colour)

when soaked in

distilled water. It

is used to test the

nature of acids and

bases. Litmus is

available as strips

of paper in red and

blue colour, and

also as a solution.

When blue litmus

is placed in an

acid it turns red.

When red litmus is

placed in a base it

turns blue

-Here it is recalled

that red, blue and

yellow are the

only three primary

colours in nature.

All other colours

are made by

mixing these three

in different

proportions.

- Also that white

and black are the

only two colours

that can be defined

scientifically as

‘white reflects

back all the light

waves, while

black absorbs all

the light waves’.

CHAPTER 5 COAL AND PETROLEUM

Q1 What are the advantageous of using LPG and CNG as fuels?

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The advantages of using LPG and CNG are that both are high octane

fuels that provide more heat or caloric value per kilogram. Both are also clean

and less polluting than fossil fuels. They can also be transported more easily

through pipes.

Q2 Name the petroleum products used for surfacing the roads.

The petroleum products used for surfacing the roads are coal-tar and

bitumen.

Q3 Describe how coal is formed from dead vegetation. What is this process

called?

The process through which dead vegetation is converted in to coal is called

‘carbonization’. About 300 million years ago the surface of the Earth was

covered with thick forests. The presence of forests caused heavy rains and

floods. The floods caused landslides that caused forests in large areas to get

buried under the soil. Forests also got buried due to earthquakes. With

successive soil deposits and floods the buried forests sank deeper below the

crust of the earth. The higher temperatures below the surface of the earth caused

the wood from the vegetation to get converted into coal.

Q 6 Explain why fossil fuels are exhaustible natural resources?

All natural resources are exhaustible. Coal and petroleum are fossil

fuels that are also exhaustible natural resources. They have been created through

the slow, natural process of carbonization due to reaction of pressure and

temperature on buried dead vegetation and animal remains.

This process took millions of years to create the fossil fuels. Also special

climatic conditions existed millions of years ago that made the process possible.

These cannot be recreated in modern times. As such if these fossil fuels are

overused, they will get exhausted and not be available in future as no fresh

stocks of such fuels are being created.

Q7 Describe characteristics and uses of coke

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Coke is the most superior quality of coal. It is tough and porous and almost

the pure form of carbon. It gives the highest caloric value of heat per kilogram.

As such it is the most expensive coal and used only in the manufacture of steel

and for the extraction of many metals from their ores.

Q8 Explain the process of formation of petroleum

For millions of years ever since the creation of Oceans, organisms and fish in

the oceans have been dying. Their remains sink to the ocean floor and

accumulate. These accumulated remains get covered with layers of sand and

clay that buries them deeper and deeper. High pressure and temperatures and

millions of years transformed the accumulated remains into petroleum and

natural gas. Due to continuous movement of the crust of the earth along the

continental belt volcanic and earthquake activities raise the ocean bed near the

coastal regions. Therefore, rich deposits of petroleum and gas reserves and are

found in many coastal areas, and on land that was under the sea millions of

years ago.

CHAPTER 6 COMBUSTION AND FLAME

Q1 List conditions under which combustion can take place

Combustion is a chemical process in which a substance reacts with

oxygen to give off heat and light. The conditions needed for combustion to take

place are the presence of oxygen, a combustible substance or an inflammable

substance and an ignition temperature.

Q3 Explain how the use of CNG in automobiles has reduced pollution in our

cities.

Air pollution is cities is caused by emission of carbon monoxide by

vehicles that use fossil fuels such as petrol and diesel. Diesel in particular is

used by buses and trucks and other heavy vehicles and is a major cause of

pollution. CNG or Compressed Natural Gas is a clean fuel because it does not

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emit any carbon-monoxide to pollute the air. Therefore its use in automobiles

can reduce air pollution is cities.

Q4 Compare LPG and wood as fuels

LPG Wood

LPG is an abbreviation that stands

for Liquefied Petroleum Gas. It is

created by subjecting gas to such

high pressure that it converts in to

liquid form.

Wood is the solid fuel grown on

mature trees in the forest.

LPG is an expensive fuel compared

to wood

Wood is a much cheaper fuel

compared to LPG

LPG needs a special gas stove for

its use

Wood can be burnt as a fuel even

on an informal way by arranging a

few piece in pile. It does not need

any special equipment or stove

LPG needs to be stored in a special

cylinder and sealed when not in use

Wood can be stored openly but

needs to be protected from rain,

because when wet it is difficult to

burn wood.

LPG does not emit any smoke

while burning and is therefore a

non-polluting fuel

Wood emits smoke while burning

and is therefore, polluting

LPG is very easy to alight and use Wood is more difficult to alight and

use

Per kg of LPG gives 55000 caloric

value

Per kg of wood gives 17000 to

22000 caloric value

Q5 Give reasons

(a) Water is not used to control fires involving electrical equipment

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Water is a good conductor of electricity. Therefore, though it is

used for controlling all other forms of fire, it is not used for

controlling fires involving electrical equipment because then in

place of cutting off the current supply it is likely to spread the

current. This can even cause death by electrocution.

(b) LPG is a better domestic fuel than wood

Liquefied Petroleum Gas is a better domestic fuel than wood

because it has a higher caloric value, is clean and non-smoky, and is

easier to use.

(c) Paper by itself catches fire easily whereas a piece of paper wrapped

around an aluminum pipe does not.

When a piece of paper is wrapped around an aluminum pipe it

reduces its temperature is lower than its ignition temperature. The

supply of oxygen on the lower surface of paper is also cut out due to

wrapping it. This further delays its combustion.

Q 7 Name the unit in which the caloric value of a fuel is expressed.

The caloric value of fuel is expressed in a unit called ‘kilojoule per kg’

which is written in abbreviation as ‘kJ / kg’

Q8 Explain how CO2 is able to control fires.

CO2 is useful for controlling fires of electrical equipment, oil and

petrol. It cuts out the supply of oxygen to the fire and thereby extinguishes it.

CO2 is stored in an extinguisher in liquid form. When released it expands in

volume and cools down. This expansion creates a blanket over the fire that cuts

out the supply of oxygen from the air.

Q9 It is difficult to burn a heap of green leaves but dry leaves catch fire

easily. Explain.

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Green leaves contain a lot of water that inhibits burning. Dry leaves become

more combustible due to absence of any water.

Q10 Which zone of a flame does a goldsmith use for melting gold and silver

and why?

A goldsmith uses the outermost zone of a flame for melting gold and

silver. The outermost non-luminous zone of the flame has the highest

temperature. Therefore, it is most effective for melting of metals such as gold

and silver.

Q11 In an experiment 4.5 kg of a fuel was completely burnt. The heat

produced was measured to be 180.000 kJ. Calculate the caloric value of the fuel.

Ans. The caloric value of the fuel is 40.00 kJ / kg.

Q12 Can the process of rusting be called combustion? Discuss.

No, the process of rusting cannot be called combustion because

combustion occurs only when burning in air is involved and both heat and light

are generated in the process. In the process of rusting iron reacts with oxygen to

create iron oxide. This does not cause any burning, or heat or light. Therefore,

rusting cannot be called combustion.

CHAPTER 11 FORCE AND PRESSURE

Answer 1 Two examples in which an object is pushed or pulled to change

the state of motion of objects are: (a) Opening and shutting of a door. (b)

Opening and shutting of a table drawer

Answer 2 Two examples of situations in which applied force causes a change

in the shape of an object are (a) pressing a balloon ( b) pressing a soft rubber

ball.

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Answer 3 Fill in the blanks : answers (a) pull (b) attracts (c) push (d) repels

Answer 4 (a) shape (b) mascular (c) non-contact (d) gravity and friction or air

Answer 5 (a) Agent are the fingers and the object is the lemon that is squeezed

and the force is muscular force

( b) Agent is the hand that presses the tube, object is the toothpaste

tube, and force applied is the muscular force.

(a) Agent is the spring, load is the object, and force is gravitational

force and non-contact force

(b) Athlete is the agent, the bar is the object and force is mascular

force.

Answer 6. It changes the shape of the piece of iron

Answer 7. Electromagnetic force is responsible for attraction between the

balloon and the wall.

Answer 8. Air pressure and gravitational force are the forces acting on the

bucket. These forces do not change the state of its motion because the object is

in a state of rest.

Answer 9. Friction and gravity are the two forces acting on the rocket

Answer 10. Is due to atmospheric pressure.

CHAPTER 12. FRICTION

Answer 8 The sliding friction is less than static friction because a sliding

object does not get sufficient time to interlock with the contact points of the

irregularities of the floor surface. When the object static its surface touching the

floor interlocks with the irregularities of the floor surface. Therefore static

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friction is more than sliding object and sliding friction is slightly less than static

friction.

Answer 9 Give examples to show that friction is both a friend and a foe

Friction is a friend because without it no control over movement

would exist. Without friction a moving person or object would have difficulty in

stopping or being in a state of rest. Also without friction it would not have been

possible to hold anything in one’s hand, or to write on a paper or a black-board.

In winter rubbing of one’s palms can help to warm them through friction.

Friction is a foe because it causes wear and tear of various objects that are

involved in any movement, such as shoes and tyres of vehicles. Friction also

damages machine parts in factories and vehicles. Due to friction more muscular

energy gets wasted.

Answer 10 Objects moving in fluids must have special shapes in order to

minimize wear and tear due to friction. Generally these shapes are spherical or

rounded as in the case of ball bearing.

CHAPTER 13

SOUND

The background context for this Chapter is given first. Also see ‘Fundamentals of

Physics’ in the Fundamental unit accessible from Home page.

All stars emit radio frequency waves along with light frequency waves.

Radio frequency waves fall in the frequency band 20 cycles per second to 107

kilocycles per second meaning 1010

cycles per second.

These waves are produced by the oscillation of a current of electrons in

specially designed circuits. Radio waves are subdivided into several groups

according to wave length or frequency.

The broad divisions are:

Wave length in

metres

Frequency, kilocycles

per second

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Audio frequencies Over 10,000 Below 30

Long and medium wave 10,000 to 100 30 to 3,000

Short wave 100 to 10 3,000 to 30,000

Very high frequency (VHF) 10 to 1 30,000 to 3 x 105

Ultra high frequency (UHF) 1 to 0.1 3x105 to 3 x 10

6

Radar frequency 0.1 to 0.01 3x 106 to 3x10

7

In the above division the lowest frequency is also called the audio frequency

because they are the frequencies of sound waves that can be detected by the

human ear.

Chapter begins here:

All Sound waves or audio frequencies have three characteristics, namely

(a) pitch

(b) loudness

(c) quality or timbre.

The (a) Pitch of a sound depends entirely on its frequency. A pure musical

note consists of one basic frequency. For example the middle note of the

‘saptasur’ has a basic frequency of 256 cycles per second. The highest note has

double this frequency.

( see Indian classical Music slide 2 under Fundamentals )

The (b) loudness of a sound is the amount of energy contained by the wave by

which it is transmitted. This is related directly to the amplitude.

The (c) quality or timbre of sound depends on the number and strength of the

overtones which are produced together with the basic frequency.

If a string or a wire is stretched, as in the case of all string musical instrument

such as a sitar or a sarod, the length, the thickness, the tension of its pull, the

division points at which it is fixed, will determine the number of overtones it

will have along with each of its fixed frequency. These overtones give the

distinguishing quality to the sound produced by different musical instruments.

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The transmission of energy through sound waves is very similar to

transmission of energy through electromagnetic waves.

The differences are :

(a) sound waves cannot be radiated through empty space. They always need

a medium of matter whether in solid form, or fluid form, or gaseous form.

(b) sound waves travel much more slowly than electro-magnetic waves or

light waves. The speed of sound waves depends on the material through which

they are traveling. They are faster in solids than in liquids and gases, and are

faster in liquids than in gases.

The velocity of sound in air at sea level is 740 miles per second.

(c) The sound waves are longitudinal waves while the electro-

magnetic or light waves are transversal waves.

(d) In the sound waves the movement of a particle is back and forth in

the same direction as the wave. In the transversal wave the

movement is at an angle.

Sound waves can be converted into electrical waves through instruments such

as a microphone.

Their volume can be increased through simple devices such as a loudspeaker.

Answer 8 Music is the pleasant frequency of sound. Musical sound

is the sound that is pleasant to hear. The human ear has an audible

range from 20 hertz to 20,000 hertz. Loudness of sound is proportional

to the amplitude of the vibration producing the sound. Loudness is

expressed in unit called decibel (dB) A whisper is sound at 30 dB while

a normal conversation is 60 dB. Above 80 dB sound becomes

physically painful. Noise is the unpleasant frequency of sound.

Excessive or unwanted sound is noise. Music also can become noise if

its loudness increases to above 80 dB

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Answer 13. Lightning is seen earlier and thunder is heard later

because the speed of light is faster than the speed of sound.

CHAPTER 14 CHEMICAL EFFECTS OF ELECTRIC

CURRENT

In the last class it was seen that in every chemical reaction

chemical energy is converted in to heat. This chapter is part of the

process of how chemical energy can be converted directly in to electric

energy.

For this, chemical reaction has to take place in an electric cell. A

simple electric cell is made by dipping a rod of zinc (Zn) and a rod of

copper (Cu) in a solution of sulphuric acid (H2SO4) in water (H2O)

Zinc dissolves in acid forming zinc ions, sulphate ions and hydrogen

ions. If the two rods are connected with a piece of metal wire the

electrons (ions) will start flow from the zinc rod to the copper rod. The

copper rod will get negatively charged. This will attract the positively

charged hydrogen ions towards the copper rod.

The two metal rods in this electric cell are called the ‘electrodes’,

and the solution is called ‘electrolyte’. Different metals chosen as

electrodes will produce different quantities of electric energy from such

a chemical reaction. Nearly all reactions that occur in the electric cell

are reversible. This means if electric energy is introduced in the

chemical reaction the reaction will go backwards. This is called the

process of ‘electrolysis’ through which gold, silver, or tin are ‘plated’

on to articles made of cheaper metals. This chapter is the first step in

understanding this process.

In general, electrical field across which energy is transmitted exists

between any two charged particles of matter. The attractive force of

two charges has the ability to bridge small gaps or distance between the

two. This results in attraction which is similar to the attraction in a

magnetic field. As a single electron behaves like a magnet, the electric

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current which is a flow of electrons also exerts a magnetic field. This is

called the electro-magnetic field.

Chapters 14 and 15 make a set and need to be understood together.

From the Chapter

Answer 6 Pure water does not conduct electricity. If it is to made a

good conductor of electricity a pinch of salt needs to be added to it to

make is a solution. All solutions whether acids, bases or salts are good

conductors of electricity. As tap water contains some mineral salts

naturally dissolved in it, ordinary water is a good conductor of

electricity.

Answer 7 Normal water is a good conductor of electricity. To

prevent damage through electric shocks, before using water hoses to

douse a fire, firemen switch off the main electric supply in the area.

Answer 9 It is not safe for the electrician to carry out electrical

repairs outdoors during heavy downpour because rainwater has several

dissolved minerals and salts which make it a good conductor of

electricity.

CHAPTER 15 SOME NATURAL PHENOMENA

Read this chapter with Chapter 14

Answer 4 Sometimes a crackling sound is heard while taking off a sweater

in winter because when the sweater is being taken off it is rubbed against the

shirt or the inner clothes. This rubbing generates a charge of static energy that

produces the crackling sound

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Answer 5 A charged body loses it charge if touched by hand because the

human body is a good conductor of electricity and the charge flows through the

hand in to the ground.

Answer 7 Three measures that can protect against lightning are (a) having a

lightning conductor installed on the roof of the house (b) Take shelter in a house

or a building and do not stay in the open. (c) In a forest take shelter under short

trees and avoid tall trees.

CHAPTER 16 LIGHT

Light is one of the six forms of energy that is useful to humans. These six

forms are (1) Chemical energy (2) Heat energy (3) Mechanical energy (4)

Electrical energy (5) Radiant energy (light) ( 6) Atomic energy. These six

forms energy can be transformed from one form to another through a variety of

complex processes through the medium of matter. If matter is absent as in outer

space, then energy can exist only in the form of radiant energy in the form of

ultraviolet rays, x-rays, y-rays, and cosmic rays. In this chapter only the first

simple rules of light and reflection are introduced, but you need to keep in mind

the larger picture. Try reading chapter 16 and chapter 17 together as these two

give the small and the larger picture about light

Light is a very small portion of radiant energy that is seen by the

human eye as the visible spectrum. The retina of the human eye is sensitive to a

very narrow waveband of 4.1 x 10-5

cm. to 6.5 x 10-5

cm. If a ray of sun light is

passed through a prism it splits up in to the range of different colour waves.

This is the structure of the ‘visible spectrum’. The wave length of red light is the

longest and therefore it is on the top of the spectrum at 6.5 x 10-5

The wave

length of violet light is the shortest and therefore it is at the lowest level at 4.1 x

10-5

Wavelengths shorter than the violet rays are not visible to the human eye and

therefore they are called ‘Ultra-violet’ rays. Though the visible spectrum shows

seven different colours they all blend and merge in to the next wave band.

Therefore, between each narrow band of the pure colour exists a band of

blended colours also

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The following table will help in understanding the relative position of the

frequencies.

TABLE OF RADIANT ENERGY WAVE FREQUENCIES

Wave

length in

metres

Frequency

in kilocycle

per second

10-15

Cosmic ray frequencies

10-14

1020

10-13

y-ray frequencies

1019

10-12

1018

10-11

x-ray frequencies

1017

10-10

1016

10-9

1015

10-8

Ultra-violet frequencies

1014

10-7

1013

10-6

Visible light 1012

10-5

Infra-red frequencies

1011

10-4

1010

10-3

Radio frequencies

109

10-2

108

10-1

107

1 106

10 105

102 10

4

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103 10

3

104

Audio frequencies

102

105 10

106 1

107 0.1

0.01

From the Chapter

Answer 2 Regular reflection takes place on smooth, polished and

regular surface. Diffused reflection takes place on irregular and rough

surface. The two laws of reflection state that a reflection takes place

when the angle of incidence is equal to the angle of reflection, and when

the reflected ray and the normal line from point of incidence fall in the

same plane. In diffused reflection these two laws do not fail, but

diffused reflection is caused by the irregularities due to the rough

surface.

Answer 3

(a) Polished wooden table: gives diffused reflection because

even after polish the irregular structure of the wood will

not enable the angle of reflection and angle of incidence

to fall on the same plane

(b) Chalk powder: gives diffused reflection because the

powder is not a plane surface

(c) Cardboard surface: will give diffused reflection due to

irregularities on the surface of the cardboard.

(d) Marble floor with water spread over it: will give regular

reflection as the water will enhance the capacity of the

polished surface to reflect

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(e) Mirror : will give a regular reflection as the angle of

reflection and the angle of incidence will be equal due to

the smooth surface of the mirror

(f) Piece of paper will give a diffused reflection as the surface

of the paper is not a polished plane surface for the purpose

of reflection.

Answer 4 The first law of reflection states that the angle of incidence is

always equal to the angle of reflection.

The second law states that the ray of incidence, the normal ray and the

reflected ray all fall in the same plane.

See Chapters on Light in ‘Fundamentals of Physics’