Question

In oscillating LC circuit, the total stored energy is $U$ and maximum charge upon capacitor is $Q .$ When the charge upon the capacitor is $\frac{Q}{2}$, the energy stored in the inductor is

• A. $\frac{U}{2}$
• B. $\frac{U}{4}$
• C. $\frac{4}{3} U$
• D. $\frac{3 U}{4}$

Answer 1

Answer: (D)

Initial energy $=$ total energy
$=\frac{Q^{2}}{2 C}=U$
$U'=\frac{Q^{2}}{4(2 C)}$
$\left(\right.$ as $\left.Q'=\frac{Q}{2}\right)$
$=\frac{Q^{2}}{8 C}$
$U_{\text {inductor }}=U_{\text {total }}-U_{\text {capacitor }}$
$=\frac{Q^{2}}{2 C}-\frac{Q^{2}}{8 C}$
$=\frac{3 Q^{2}}{8 C}=\frac{3}{4} U$