If the resistance doubles while the voltage stays the same, what effect will that have on the power?

A. It will increase by a factor of 2.

B. It will decrease by a factor of 2.

C. It will increase by a factor of 4.

D. It will decrease by a factor of 4.

The best formula to use for this question is

Power = (voltage) ² / R

So Original power = (voltage) ² / (original R)

and

New power = (same voltage) ² / (2 x original R)

That's equal to (1/2) (voltage) ² / (original R)

which is equal to (1/2) (original power).

So I guess the power decreases by half, and that's choice-B.