A light bulb,sold as long-lasting,is rated 100 W at 130 V.The "increased" lifetime comes from using it at 120 V.Assuming negligible change in resistance at the different voltage,what is its power consumption at 120 V?

Question

Quizplus · Accepted Answer

Power is given by P = V^2/R. Since R is constant, P is proportional to V^2. Therefore, at 120 V, the power consumption will be (120/130)^2 * 100 W = 85.4 W.

A Light Bulb,sold as Long-Lasting,is Rated 100 W at 130