A permanent magnent has the shape of a sufficiency thin disc magnetized along its axis. The radius of the disc is `R = 1.0 cm`. Evaluate the magnitude of a molecular current `I'` flowing along the rin of the disc, lying at a distance `x = 10 cm` from its centre, is equal to `B = 30 muT`.

Explanation

From 3.270, for `x gt gt R`
`B_(x) = (mu_(0) I' R^(2))/(2x^(3))`
or, `I'' = (2B_(x) x^(3))/(mu_(0) R^(2)) = (2xx3xx10^(-5) xx T xx (10^(-1) m)^(3))/(1.26xx10^(-6)xx(10^(-2) m)^(4)) = 0.5 kA`