The expression for the magnetic energy stored in a solenoid in terms of magnetic field \(B\), area \(A\) and length \(l\) of the solenoid is:

The ratio of magnetic energy per unit volume and electrostatic energy stored per unit volume in a parallel plate capacitor is:
1. \(\left(\dfrac{1}{\varepsilon_0 \mu_0}\right)\dfrac{B^2}{E}\)

2. \(\left(\dfrac{1}{\varepsilon_0 \mu_0}\right)\dfrac{E^2}{B}\)

3. \(\left(\dfrac{1}{2\varepsilon_0 \mu_0}\right)\dfrac{B^2}{E}\)

4. \(\left(\dfrac{1}{2\varepsilon_0 \mu_0}\right)\dfrac{E^2}{B}\)$\mathrm{}$