A permanent magnety is shaped as a ring with a narrow ghap between the poles. The mean diameter of the ring equals `d = 20 cm`. The width of the gap is equal to `b = 2.0 mm` and the magnetic induction in the gap is equal to b = 40mT'. Assuming that the scattering of the magnetic flux at the gap edges is negligible, find the modulus of the magnetic fleid strength vector inside the magnet.

Explanation

We use, `oint vec(H).d.vec(l) = 0`
Neglecting the fringing of the lines of forces, we write this as
`H (pi d - b) + (B)/(mu_(0)) b = 0`
or, `H = (-Bb)/(mu_(0) pi d) = 101 A//m`
The sense of `H` is opposite to `B`