Basic Electrical Engineering MCQs Part 15

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Basic Electrical Engineering MCQs Part 15

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. 1:2
  3. 2:1
  4. 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:

  1. The bright bulb
  2. The dim bulb
  3. Both have same resistance
  4. 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:

  1. 24.39%
  2. 34.92%
  3. 54.88%
  4. 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:

  1. 50 W has thicker filament
  2. 100 W has thicker filament
  3. Both have filaments of same thickness
  4. 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. 1%
  2. 2%
  3. 3%
  4. 99%

Correct answer: 1. 1%

Explanation: P = V²/R.

Less current means more resistance.

This in turn means less power for given voltage.

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