Question

If 125V is applied across a 250V, 100W incandescent bulb, the power consumed will be _____ .

• A. 25 W
• B. 50 W
• C. 100 W
• D. 12.5 W

Hint:

The power consumed by a bulb is proportional to the square of the voltage applied. If the voltage is reduced, the power consumed decreases by the square of the ratio of the voltages.

Answer 1

The Correct Option is A

The power consumed by a bulb is given by the formula: \[ P = \frac{V^2}{R} \] Where: - \( V \) is the voltage across the bulb,
- \( R \) is the resistance of the bulb.
First, calculate the resistance of the bulb using the rated values: \[ R = \frac{250^2}{100} = \frac{62500}{100} = 625 \, \Omega \] Now, apply the reduced voltage (125V) and calculate the power: \[ P = \frac{V^2}{R} = \frac{125^2}{625} = \frac{15625}{625} = 25 \, \text{W} \] Thus, the power consumed by the bulb when 125V is applied is 25 W, which is option (1).