When a 12.0 V car battery runs a single 30.0 W headlight, how many electrons pass through it each second?

Strategy

To find the number of electrons, we must first find the charge that moved in 1.00 s. The charge moved is related to voltage and energy through the equation ΔPE =qΔV. A 30.0 W lamp uses 30.0 joules per second. Since the battery loses energy, we have ΔPE = -30.0 J and, since the electrons are going from the negative terminal to the positive, we see that ΔV = +12.0 V.