# Electricity

## Exemplar Problem

### Multiple Choice Questions 2

Question 10. A cylindrical conductor of length l and uniform area of cross section A has resistance R. Another conductor of length 2l and resistance R of the same material has area of cross section

1. A/2
2. (3A)/2
3. 2A
4. 3A

Question 11. A student carries out an experiment and plots the V-I graph of three samples of nichrome wire with resistances R1, R2 and R3 respectively. Which of the following is true?

1. R1 = R2 = R3
2. R1 > R2 > R3
3. R3 > R2 > R1
4. R2 > R3 > R1

Answer: (c) R3 > R2 > R1

Question 12. If the current I through a resistor is increased by 100% (assume that temperature remains unchanged), the increase in power dissipated will be

1. 100 %
2. 200 %
3. 300 %
4. 400 %

Question 13. The resistivity does not change if

1. the material is changed
2. the temperature is changed
3. the shape of the resistor is changed
4. both material and temperature are changed

Answer: (c) the shape of the resistor is changed.

Question 14. In an electrical circuit three incandescent bulbs A, B and C of rating 40 W, 60 W and 100 W respectively are connected in parallel to an electric source. Which of the following is likely to happen regarding their brightness?

1. Brightness of all the bulbs will be the same
2. Brightness of bulb A will be the maximum
3. Brightness of bulb B will be more than that of A
4. Brightness of bulb C will be less than that of B

Answer: (c) Brightness of bulb B will be more than that of A

Question 15. In an electrical circuit two resistors of 2 Ω and 4 Ω respectively are connected in series to a 6 V battery. The heat dissipated by the 4 Ω resistor in 5 s will be

1. 5 J
2. 10 J
3. 20 J
4. 30 J

Explanation: Since, resistors are connected in series, thus total effective resistance in circuit = 2Ω + 4Ω = 6Ω

Since,I= V/R

Therefore,electric current,I through the circuit =(6V)/(6Ω)=1 A

Now,voltage through,4Ω resistor

Since,I= V/R

Therefore,1A= V/(4Ω)

Therefore,V=4V

Now, given, time, t = 5s

Dissipation of heat by 4Ω

Since, there is no division of electric current when resistors are connected in series,

Thus, electric current, I = 1A

Since,H= I^2 Rt

⇒H=(1A)^2xx4Ωxx5s

⇒H=1xx4xx5 joule

⇒H=20 joule

Question 16. An electric kettle consumes 1 kW of electric power when operated at 220 V. A fuse wire of what rating must be used for it?

1. 1 A
2. 2 A
3. 4 A
4. 5 A

Explanation: Given, power, P = 1 kW = 1000 W

Since, electric power, P = V xx I

Or, 1000 W = 220V xx I

Therefore,I=(1000W)/(220V)=4.54 A

Thus, an fuse of rating 5A must be used.

Question 17. Two resistors of resistance 2 Ω and 4 Ω when connected to a battery will have

1. same current flowing through them when connected in parallel
2. same current flowing through them when connected in series
3. same potential difference across them when connected in series
4. different potential difference across them when connected in parallel

Answer: (b) same current flowing through them when connected in series

Question 18. Unit of electric power may also be expressed as

1. volt ampere
2. kilowatt hour
3. watt second
4. joule second