Q: The mean electric energy density between the plates of charged capacitor is (here , q = charge on capacitor , A = Area of capacitor plate )

(a) $\large \frac{q^2}{2 \epsilon_0 A^2} $

(b) $\large \frac{q}{2 \epsilon_0 A^2} $

(c) $\large \frac{q^2}{2 \epsilon_0 A} $

(d) None of above

Sol: $\large Energy \; density = \frac{Energy}{volume} = \frac{U}{V}$

$\large u = \frac{\frac{q^2}{2 C}}{A d} = \frac{q^2}{2 \frac{\epsilon_0 A}{d} A d} $

$\large = \frac{q^2}{2 \epsilon_0 A^2}$

Ans: (a)