AP Physics C E and M

Question

A capacitor has been charged by connecting it to a 12 V battery. How much work was done in charging this capacitor, if at the end of charging, its charge is 2 μC?

Group of answer choices

7 μJ

12 μJ

14 μJ

23 μJ

Answer 1

You can use the Work/Energy Theorem to calculate the answer here. Since work done is equal to change in energy, if you calculate the energy in the capacitor you will know how much work was done.

To calculate the energy stored in a capacitor, you use the equation Uc = 1/2 * V² * C

So for this problem, the energy in the capacitor, and therefore the work done to charge that capacitor is:

1/2 * 144 * 2*10^-6 = 144 * 10^-6

= 144 µJ (OR 140 µJ if you use 2 sig figs)

I see this is not one of your answer choices, but I hope this helps!

Answer 2

E=.5*Q*V = 12 micro joules