A bulb is designed for 100 W at 130 V rms. What is the power dissipated by this bulb if it is used in a 120 V rms circuit?
A) 169 W
B) 130 W
C) 100 W
D) 85 W
E) it will blow out

Question

Quizplus · Accepted Answer

The power dissipated by the bulb is given by:

P = V^2/R

where V is the voltage applied to the bulb and R is the resistance of the bulb.

We know that the bulb is designed for 100 W at 130 V rms. So, we can find the resistance of the bulb using the above equation as:

100 = 130^2/R
R = (130^2)/100 = 169 Ohm

Now, if the bulb is used in a 120 V rms circuit, the power dissipated by the bulb can be calculated as:

P = V^2/R = (120^2)/169 = 85 W

Therefore, the answer is D.

A Bulb Is Designed for 100 W at 130 V