# Energy stored in a toroid

by Reshma
Tags: energy, stored, toroid
 P: 777 Calculate the energy stored in a toroidal coil. The magnetic field in a toroid is give by: $B = \frac{\mu_0 n I}{2\pi r}$ Energy stored is given by: $$W = {1\over 2\mu_0}\int B^2 d\tau$$ $$W = {1\over 2\mu_0} \frac{\mu_0^2 n^2 I^2}{4\pi^2}\int {1\over r^2}d\tau$$ How do I determine the volume element for a toroid?