# 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?
 Sci Advisor HW Helper P: 1,930 The toroid can usually be approximated by a solenoid of length 2\pi R, with r constant inside the toroid. Then V=(2\pi L)*(\pi a^2), with B constant.

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