If the charge on a capacitor is increased by 2 coulomb, the energy stored in it increases by 21%. The original charge on the capacitor is

Options

A. 10 C
B. 20 C
C. 30 C
D. 40 C

Answer

B

Explanation

`U=Q^2/(2C)implies U prop Q^2`
`implies U_1/U_2=Q^2/((Q_2+2)^2)impliesU/(1.21U)=Q^2/((Q+2)^2)`
`impliesQ/(Q+2)=sqrt(1/(1.21))implies Q/(Q+2)=1/(1.1)`
`implies Q + 2 = Q(1.1) implies 0.1Q = 2 implies Q = 20C.`