# Solved Problems-13

Problem-13
Obtain an expression for the self-inductance of a toroid of circular section with â€˜Nâ€™ closely spaced turns.
Solution
Let,
r = Mean radius of the toroid
N = Number of turns
S = Radius of the coil

We have the magnetic field,

total flux linkage per turn is,

Hence, the self-inductance of the toroid is