Electric potential energy? Capacitance?

Question

a. Calculate the electric potential energy stored in a 1.7 × 10–11 F capacitor that stores 3.40 × 10–10 C of charge at 20.0 V.

 

b. Calculate the capacitance of a system that stores 8.0 × 10–10 C of charge at 25.0 V.

Answer 1

(a)

 

U = (1/2) * C * V^2 = (1/2) (1.7 x 10^-11) (20)^2 J = 3.4 x 10^-9 J

 

(b) 

 

C = Q/V = (8 x 10^-10) / (25) F = 3.2 x 10^-11 F