A current of \(\frac{1}{3\pi}\,A\) passes through an ideal toroid of 900 turns per metre. If the relative permeability of the material of the core of the toroid is 400, then the magnetic field inside the core of the toroid is:
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For an ideal toroid:
\[
B=\mu_0\mu_r nI.
\]
It is analogous to the magnetic field inside a solenoid.