Problem 3.272

A permanent magnet has the shape of a sufficiently thin disc magnetized along its axis. The radius of the disc is $R=1.0 \mathrm{~cm} .$ Evaluate the magnitude of a molecular current $I^{\prime}$ flowing along the rim of the disc if the magnetic induction at the point on the axis of the disc, lying at a distance $x=10 \mathrm{~cm}$ from its centre, is equal to $B=30 \mu \mathrm{T}$