Question

in an oscillating L-C circuit , the maximum charge on the capacitor is Q. the charge on the capacitor , when the energy is stored equally between the electric and magnetic field is

1) Q/2

2) Q/(2)^1/2

3) Q/(3)1/2

4) Q/3

Answer 1

The electric energy stored when energy in equally distributed, $U{\text{'}}_E=\frac{1}{2}\frac{q^2}{C}$
The energy stored in the capacitor when it is maximally charged, $U_E=\frac{1}{2}\frac{Q^2}{C}$
Now
$$\begin{gathered} U_E=2U{\text{'}}_E \\ \Rightarrow q=\frac{Q}{\sqrt{2}} \end{gathered}$$
so 2 is the right answer.