ELECTRICITY

1 mark questions

1. What happens to the resistance of the wire when it is made thinner?

2. Why is resistance less when resistors are joined in parallel?

3. What are the special features of a heating wire?

4. Name a few metals which offer higher resistance to the passage of electricity

than copper?

5. Out of 60W and 40W lamps, which one has a higher electrical resistance

when in use?

6. Why are coils of electric toasters made of an alloy rather than a pure metal?

7. Why copper wires are used as conducting wires?

8. What is the change in the resistance of a metal wire if its radius is halved and

length is made one-fourth of its original length?

9. What is the conventional direction of electric current?

10.How much work is done when 1 charge moves against a potential

difference of 2V?

11.Name the factors on which the power consumed by an electrical appliance

depends.

12.What is the meaning of the symbol kWh? Which quantity does it depend?

13.Why is an electric bulb filled with argon or nitrogen, but not with air?

14.Why is much less heat generated in long electric cables than that in filaments

of electric bulbs?

15.Why does the cord of an electric heater not glow while the heating element

does?

16.The electrical resistivity of few materials is given below in ohm-meter. Which

one of these materials has the highest electrical conductivity?

A B C D E F

2 Mark Questions

17.What is meant by the statement that the potential difference between two

points is 1V?

18.What are the advantages of connecting electrical devices in parallel with a

battery instead of connecting them in series?

19.Explain why an electric bulb becomes dim when an electric heater in parallel

circuit is made on. Why dimness decrease after some time?

20.Two students perform the experiments on series and parallel combinations of

two given resistors R1 andR2 and plot the following VI graphs.

21.A household uses the following electric appliances:

(i)Refrigerator of rating 400 W for ten hours each day.

(ii) Two electric fans of rating 80 W each for twelve hours each day.

(iii) Six electric tubes of rating 18 W each for 6 hours each day.

Calculate the electricity bill of the household for the month of June if the cost

per unit of electric energy is Rs. 3.00.

22.Heat is generated continuously in an electric heater but tits temperature become constant after some time. Why?

23.A wire of 1m long, 0.2 mm in diameter and ahs a resistance of 10. Calculate the resistivity of its material.

24.(i)How much current will an electric bulb draw from a 220V source, If the

resistance of the bulb filament is 1200 ? (ii) How much current will an electric heater coil draw from a 220V source, if

the resistance of the heater coil is 100? 25.Given n resistors each of resistance R, how will you combine them to get the

maximum and minimum effective resistance? What is the ratio of maximum to minimum resistance?

26.A 60W and 100W bulbs are given. Which one will be brighter when they are

connected in (i)series and (ii)parallel. 27. In a factory an electric bulb of 500 W is used for 2 hours and an electric

motor of 0.5 horse power is used for 5 hours every day. Calculate the cost of

using the bulb and the motor for 30 days if cost of electrical energy is three rupees per unit?

28.What is the equivalent resistance of this resistance combination? Here all

three resistors are 33 k. Remember to input your answer in ohms.

29.What is the equivalent resistance of the combination of resistors?

3 Mark Questions

31.A current of I ampere flows in a series circuit containing an electric lamp and

a conductor of 5 when connected to a 10V battery? Calculate the resistance of the electric lamp. Now if a resistance of 10 is connected in parallel with the series combination, what change(if any) in current flowing through 5

conductor and potential difference across the lamp will take place? Give

reason. 32.(i) A 100 W electric bulb is connected to 220 V mains power supply. Calculate

the strength of the electric current passing through the bulb. (ii) If the same

bulb is taken to U.S.A where the main power supply is 110 V, how much

electric current will pass through the bulb when connected to mains? 33.The electric power consumed by a device may be calculated by using either

of the two expressions P = 12R or P = . The first expression indicates that it

is directly proportional to R whereas the second expression indicates inverse proportionality. How can the seemingly different dependence of P on R in

these expressions be explained?

34.An electrician puts a fuse of rating 5A in that part of domestic electrical circuit in which an electrical heater of rating 1.5kW, 220V is operating. What

is likely to happen in this case and why? What change, if any, needs to be

made?

35.Three incandescent bulbs of 100W each are connected in series in an electrical circuit. IN another circuit another set of three bulbs of the same

wattage are connected in parallel to the same source. (a) Will the bulb in the

two circuits glow with same brightness. Justify your answer. (b) Now let one bulb in both the circuits get fused. Will the result of the bulbs continue to

glow in each circuit? Give reason.

36.Calculate equivalent resistance of the given circuit

37.The resistors placed in parallel have the same resistance. Determine the

current in and the voltage drop across each resistor.

Multiple Choice Questions

37.Conventionally the direction of the current is taken as

(a) the direction of flow of negative charge

(b) the direction of flow of atoms

(c) the direction of flow of molecules (d) the direction of flow of positive charge

38.If a wire of resistance 1 is stretched to double its length, then the resistance will become

(a)1/2 (b) 2 (c) 1/4 (d)4

39.The work done in moving a unit positive charge across two points in an

electric circuit is a measure of (a)current (b)resistance (c)power (d)potential difference

40. In our houses all electrical devices operate on 220V. It implies that (a)they are connected in parallel

(b)they are connected in series

(c)they all have currents of equal values (d)they all have the same resistance

41. Which of the following statements is not true, regarding the electrical setup

for the verification of Ohms law? (a)the voltmeter is connected in parallel with the known resistance.

(b)the ammeter is connected in series circuit.

(c)the rheostat can only increase the resistance in electric circuit. (d)the single key is used to switch on/off the electric circuit.

42.Which of the following laboratory apparatus is not used during the verification of Ohms law? (a)voltmeter (b)ammeter

(c)galvanometer (d)rheostat

43.The effective resistance of a circuit containing resistances in parallel is

(a)equal to the sum of the individual resistances

(b)smaller than any of the individual resistances (c)greater than any of the individual resistances

(d)sometimes greater and sometimes smaller than the individual

resistances 40.A person connects four 1/4 cells in series but one cell has its terminals

reversed. The external resistance is 1.If each cell has an emf of 1.5V, the current flowing is

(a)4/3A (b)3/4A (c)1.5A (d)zero.

41.A man has five resistors each of value 1/5. What is the maximum resistance

of the can obtain by connecting them?

(a)1 (b) 5 (c) 1/2 (d) 2/5

42.What is the minimum resistance that one can obtain by connecting all the

five resistances given in above question?

(a) 1/10 (b) 1/5 (c) 1/50 (d) 1/25

MAGNETIC EFFECTS OF ELECTRIC CURRENT

1 Mark Questions

1. Give three properties of magnetic filed lines. 2. In an electric generator one form of energy is converted into another. Name

the two forms of energy.

3. State one advantage of alternating current over direct current.

4. How can it be shown that magnetic field exists around a wire through which a direct electric current is passing?

5. What is the magnetic effect of electric current?

6. How is the strength of the magnetic field at a point near a wire related to the strength of electric current flowing in the wire?

7. What kind of magnetic field is produced by a solenoid?

8. What does the degree of closeness of the field lines signify? 9. What is the meaning of 50Hz of an ac supply?

10.Which human body parts produce magnetism?

11.On what factors does the force on a current carrying conductor placed in a

magnetic field depend? How can you increase the force? 12.Why does a compass needle show deflection when brought near a bar

magnet?

2 Mark Questions

13.What is the difference between a direct current and an alternating current?

How many times does AC used in India change direction in one second?

14.In what way the magnitude of induced current be increased?

15.Define SI unit of magnetic field. Under what condition does a moving charge experience (i) maximum force (ii) minimum force?

16.A fixed wire AB carries a current I. An electron is moving parallel to the wire.

In which direction does the electron tend to move? 17.Draw a sketch of the pattern of field lines due to a (i) current flowing in

circular coil (ii) solenoid carrying current.

18.How is the direction of magnetic field at a point determined? What is the direction of magnetic field at the centre of a current carrying circular loop?

19.Name four devices in which electric motors are used?

20.Two circular coils A and B are placed close to each other. If the current in the

coil A is changed , will some current be induced in the coil B? Give reason. 21.When does an electric short circuit occur?

22.A cylindrical bar magnet is kept along the axis of a circular coil. Will there be

a current induced in the coil, if the magnet is rotated about the axis?

3 Mark Questions

23.Explain what is overloading in an electric supply. 24.What is a solenoid? Draw a sketch to show to show the magnetic field lines

produced by a current carrying solenoid.

25.A coil of copper wire is connected to a galvanometer. What would happen if a bar magnet is (i) pushed into the coil with its north pole entering first. (ii)

held at rest in the coil.(iii) pulled out again.

26.Draw an appropriate schematic diagram showing common domestic circuits and discuss the importance of fuse. Why is it that a burnt out fuse should be

replaced by another fuse of identical rating?

27.Explain different ways to induce current in a coil.

28.What is the function of an earth wire? Why is it necessary to earth the

metallic appliances? 29.What are magnetic field lines? How is the direction of a magnetic field at

appoint determined? Mention important properties of magnetic field lines.

30.Consider a circular loop of wire lying in the plane of the table. Let the current

pass through the loop clockwise. Apply the right hand rule to find out the direction of the magnetic field inside and outside the loop.

Multiple Choice Questions

31.A magnetic field can exert force on

(a)a moving magnet (b) stationary magnet

(c)moving charge (d)all of these

32.Magnetic lines of force

(a)have more directions

(b)have no physical reality

(c)can be used to indicate the direction of the magnetic field of a point

(d)all the above

33.When is the back emf of an electric motor the greatest?

(a)when the motor is witched on

(b)when the motor is speeding up

(c)when the motor is at maximum speed

(d)when the motor is slowing down

34.According to international convention of color coding in a wire

(a)live is red, neutral is black and earth is green

(b) live is brown, neutral is blue and earth is green

(c) live is brown, neutral is green and earth is black

(d)live is red, neutral is yellow and earth is blue

35.An electric current can be produced in a closed loop

(a)by connecting it to a battery, but not by moving a magnet near it

(b)by moving a magnet near it, but not by connecting it to a battery

(c)by connecting it to a battery, as well as by moving a magnet near it

(d)neither by connecting it to battery nor by moving a magnet near it

36.Which of the following describes the common domestic power supplied in India?

(a)220V,100Hz (b)110V,100Hz

(c)220V,50Hz (d)110V,50Hz

37.Magnetic field due to a current carrying straight wire depends on

(a)current only (b)distance from the wire only

(c)both 9a) and (b) (d)none

38.The direction of the magnetic field produced by a current carrying straight

conductor can be found using

(a)right hand thumb rule (b)right hand Flemings rule

(c)left hand Flemings rule (d)right hand screw rule

39.A rectangular coil of copper wires is rotated in a magnetic field. The direction of the induced current changes once in each

(a)two revolution (b)one revolution

(c)half revolution (d)one-forth revolution

40.Electric motor

(a)is based on electromagnetic induction

(b)converts kinetic energy into electrical energy

(c)converts electric energy into kinetic energy

(d)none

41.To convert ac generator into dc generator

(a)split ring type commutator must be used

(b)slip rings and brushes must be used

(c)a stronger magnetic field has to be used

(d)a rectangular wire loop has to be used

42.Choose the incorrect statement

(a)The direction of magnetic field at a point is taken to be the direction in

which north pole of magnetic compass needle points

(b)magnetic field lines are closed curves

(c)If magnetic field lines are parallel and equi distant, they represent zero

field strength

(d)relative strength of magnetic field is shown by the degree of closeness of

the field lines.

43.Force on a current conductor in a magnetic field depends on

(a)length of the conductor (b)current in the conductor

(c)magnitude of the magnetic field (d)all of these

44.Magnetic field inside a solenoid is

(a)non-uniform (b)circular

(c)uniform (d)none

45.Magnetic field lines due to a bar magnet is similar to that of a

(a)current carrying straight wire (b)solenoid

(c)two parallel wires (d)none

SOURCES OF ENERGY

1 Mark Questions

1. Which of the following are renewable and which are non-renewable

sources of energy? Coal, wind, tides, Sun, petrol, bio-mass, hydro energy

2. Give an example of direct harnessing of solar energy.

3. In which year was the first practical solar cell made?

4. Name the constituents of bio- gas. 5. What is the minimum wind velocity required for obtaining useful energy

with a windmill?

6. What is the range of wavelength of electromagnetic waves that constitute visible radiation?

7. What is nuclear energy?

8. Though a hot iron emits radiation, yet it is not visible in the dark, why? 9. What is the function of boron rods in nuclear reactor?

10.Name an energy source which you consider the best. Give reason to your

choice.

11.Why is charcoal better fuel than coal? 12.Comment on the statement Fossil fuels are non-renewable 13.What is charcoal? How is it produced?

2 Mark Questions

14.Explain why a sheet of glass plate is used in solar heating devices. 15.State two advantages and disadvantages of geo thermal energy.

16.State important uses of solar cells.

17.Compare and contrast fossil fuels and the Sun as the direct source of

energy. 18.Why is tidal energy not likely to be a potential source of energy?

19.Explain how the energy of flowing water related to solar energy.

20.How is electrical energy generated from nuclear reactors? 21.How is petroleum gas obtained? Name the gas that is its main constituent.

22.Explain the principle of working of a windmill.

23.What is the fuel used in (i)nuclear reactor and (ii)Sun? 24.Can any source of energy pollution free. Explain your answer.

25.Suggest at least four steps to reduce energy consumption.

26.When we harness wind energy, we are harnessing solar energy. Explain.

27.Mention any two advantages and disadvantages of producing hydroelectricity by building dams on rivers.

28.What kind of mirror- concave, convex or plane would be best suited for

use in a solar cooker.

3 Mark Questions

29.Describe the steps involved in obtaining bio-gas and explain what is meant by anaerobic decomposition.

30.What is the importance of hydro power plants in India?

31.Differentiate between box type solar cooker and spherical reflector type solar cooker.

32.What will be your choice of good fuel if you lived (i) in a forest, (ii)in a

remote mountain village, (iii) in New Delhi, (iv) five centuries ago.? Why is your choice different in each case?

33.Briefly discuss three principles based on which electricity can be generated

from ocean.

34.What are the problems created by the increased demand of energy?

Suggest some method to solve them.

Multiple Choice Questions

35.The temperature range of box type solar cooker is

(a) 600C to 1800C (b) 1400C to 2000C

(c) 1000C to 200C (d) none

36.Fuel used in thermal power plants are

(a)water (b)uranium (c)biomass (d)fossil fuels

37.Minimum wind velocity required for a functional wind mill is about

(a)15m/s (b)15km/hr (c)18m/s (d)10km/hr

38.In hydroelectric power plant

(a)potential energy possessed by stored water is converted into electriity

(b)kinetic energy possessed by stored water is converted into potential

energy

(c)electricity is extracted from water

(d)water is converted into steam to produce electricity

39.The main constituent of biogas is

(a)methane (b)carbondioxide

(c)hydrogen (d)hydrogen sulphide

40.When we use biomass to generate electricity, we convert which form of energy locked in the biomass to electrical energy?

(a)chemical energy (b)kinetic energy

(c)nuclear energy (d)potential energy

41.The temperature of the material undergoing nuclear fusion should be

(a)100K (b)104 K (c)107 K (d)10K

42.In India Uranium is found in

(a)MP (b)Jharkhand (c)Orissa (d)UP

43.To keep the chain reaction in a nuclear reactor under control, one uses

(a)control rods (b)reactor core (c)coolant(d)moderator

44.To produce biogas in a biogas plant, we need

(a)air but not water (b)water but not air

(c)air and water (d)neither air not water