Basic Electrical Engineering MCQs Part 15

Contents

- 1 Two electric bulbs having resistances in ratio 1:2 are connected in parallel to a constant voltage source. The power dissipated by the bulbs are in ratio
- 2 Of two bulbs in a house, one glows brighter than the other, which of the two has larger resistance
- 3 A 1000 W heater is designed to operate of 230 V line. If line voltage drops to 200 V, the percentage drop is heat output is
- 4 Two electric bulbs have tungsten filament of same length. If one of them gives 50 W and other one 100 W, then which of following is correct:
- 5 The filament of bulb having low resistance is thicked. Sice l is constant in both cases. The 100 W bulb has less resistance as compared to 50 W. Hence, 100 W has thicker filament

## Two electric bulbs having resistances in ratio 1:2 are connected in parallel to a constant voltage source. The power dissipated by the bulbs are in ratio

Two electric bulbs having resistances in ratio 1:2 are connected in parallel to a constant voltage source. The power dissipated by the bulbs are in ratio:

- 1:1
- 1:2
- 2:1
- None of these

Correct answer: 3. 2:1

## Of two bulbs in a house, one glows brighter than the other, which of the two has larger resistance

Of two bulbs in a house, one glows brighter than the other, which of the two has larger resistance:

- The bright bulb
- The dim bulb
- Both have same resistance
- Brightness is independent of resistance

Correct answer: 2. The dim bulb

## A 1000 W heater is designed to operate of 230 V line. If line voltage drops to 200 V, the percentage drop is heat output is

A 1000 W heater is designed to operate of 230 V line. If line voltage drops to 200 V, the percentage drop is heat output is:

- 24.39%
- 34.92%
- 54.88%
- 65.68%

Correct answer: 1. 24.39%

Solution:

P = 230²/R

P’ = 200²/R

————–

P’/P = (200/230)²

————–

%age drop in heat output = (1 – P’/P) * 100

[1 – (200/230)² ]* 100 = 24.39%

## Two electric bulbs have tungsten filament of same length. If one of them gives 50 W and other one 100 W, then which of following is correct:

Two electric bulbs have tungsten filament of same length. If one of them gives 50 W and other one 100 W, then which of following is correct:

- 50 W has thicker filament
- 100 W has thicker filament
- Both have filaments of same thickness
- Insufficient information

Correct answer: 2. 100 W has thicker filament

Solution:

From formula:

R = ρl/a

## The filament of bulb having low resistance is thicked. Sice l is constant in both cases. The 100 W bulb has less resistance as compared to 50 W. Hence, 100 W has thicker filament

The filament of bulb having low resistance is thicked. Sice l is constant in both cases. The 100 W bulb has less resistance as compared to 50 W. Hence, 100 W has thicker filament.

Two electrical appliances are connected in parallel to constant voltage supply. If current in one appliance is less than second appliance by 1%, then power of first appliance will be less by what percentage:

- 1%
- 2%
- 3%
- 99%

Correct answer: 1. 1%

Explanation: P = V²/R.

Less current means more resistance.

This in turn means less power for given voltage.