Question

A solenoid of length 2.2 m has a diameter of 0.9 m. The magnetic field at its centre is 0.4 tesla. Estimate the energy stored in the field of this coil. 

Answer 1

The energy stored in the solenoid is

$U=\frac{B^2 Al}{2 \mu_0}$

$=\frac{B^2 \pi r^2l}{2 \mu_0}$ $=\frac{(0.4)^2 \pi (0.45)^2(2.2)}{2 (4 \pi \times10^{-7})}$ $=2.23 \times 10^5 J$