Electrical Engineering Questions and Answers

1. A kilowatt hour is the unit of

(i) energy
(ii) power
(iii) electric charge
(iv) electric current

2. Heat produced in a conductor depends

(i) inversely on time
(ii) directly on time
(iii) both (i) and (ii)
(iv) none of the above

3. If potential difference across a conductot of a material of resistivity ρ remains constant, then heat produced in the conductor is proportional to

(i) ρ
(ii) ρ²
(iii) 1/√ρ
(iv) 1/ρ

4. One kilowatt hour is equal to

(i) 36 x 10³J
(ii) 10³J
(iii) 36 x 10⁵ J
(iv) 10⁵ J

5. The heater element in an electric iron is made of

(i) nichrome
(ii) iron
(iii) tungsten
(iv) constantan

6. The current in a 960 W, 240 V heater operated at 200 V is

(i) 0.25 A
(ii) 3/10 A
(iii) 2.5 A
(iv) 10/3 A

7. Three electric bulbs 40 W, 60 W and 100 W are designed to work on a 220 V mains. Which bulb will burn most brightly if they are connected in series across 220 V mains?

(i) 60 W
(ii) 40 W
(iii) 100 W
(iv) all bulbs will bum equally brightly

8. Two electric bulbs have tungsten filament of the same length. If one of them gives 60 W and the other 100 W, then,

(i) 100 W bulb has thicker filament
(ii) 60 W bulb has thicker filament
(iii) both filaments are of the same thickness
(iv) information insufficient

9. Two electric lamps of 40 W each are connected in parallel. The power consumed by the combination is

(i) 20 W
(iii) 80 W
(ii) 60 W
(iv) 100 W

10. The time required for 1kW heater to raise the temperature of 10 litres of water through 10°C is

(i) 210 sec
(ii) 840 sec
(iii) 42 sec
(iv) 420 sec

11. The electric lamps 40 W, 220 V each are connected in series across 220 V. The power consumed by the combination is

(i) 80 W
(ii) 20 W
(iii) 160 W
(iv) 40 W

12. Two bulbs, 100 W, 250 V and 200 W, 250 V, am connected in parallel across a 500 V line. Then,

(i) 100 W bulb will be fused
(ii) 200 W bulb will be fused
(iii) Both bulbs will be fused
(iv) No bulb will be fused

13. Two bulbs, 100 W, 250 V and 200 W, 250 V are connected in series to a 500 V line. Then,

(i) 100 W bulb will be fused
(ii) 200 W bulb will be fused
(iii) both bulbs will be fused
(iv) no bulb will be fused

14. Three bulbs B₁, B₂ and B₃ are connected to the mains as shown in above Fig. If B₃ is disconnected from the circuit by opening switch S, then incandensence of bulb B₁ will

(i) decrease
(i) increase
(iii) No change
(iv) cannot say

15. You are given the following electrical appliances (a) 1 kW, 250 V electric heater (b) 1 kW, 250 V, electric kettle (c)1 kW, 250 V, electric bulb. Which of these has the highest resistance ?

(i) heater
(ii) kettle
(iii) bulb
(iv) all have equal resistances

16. If current in an electric bulb drops by 2%, then power decreases by

(i) 2%
(ii) 4 %
(iii) 1 %
(iv) 16%

17. Two bulbs of 500 W and 300 W are manufactured to operate on 220 V line. The ratio of resistance of 500 W bulb to that of 300 W bulb is

(i) 5 : 3
(ii) 9 : 25
(iii) 3 : 5
(iv) 25 : 9

18. The same mass of copper is drawn into two wires 1 mm thick and 3 mm thick. Two wires are connected in series and current is passed. Heat produced in the wires is in the ratio

(i) 81 : 1
(ii) 1 : 81
(iii) 3 : 1
(iv) 9 : 1

19. The power of a heater is 500 W at 800°C. What will be its power at 200°C ? Temperature coefficient of resistance is 4 x 10^-4/^oC.

(i) 484 W
(ii) 672 W
(iii) 526 W
(iv) 620 W

20. A constant voltage is applied between two ends of a uniform metallic wire. Some heat is developed. If both length and radius of wire are halved, the heat developed in the same duration is

(i) half
(ii) twice
(iii) one-fourth
(iv) same