A Rowland ring of mean radius 15 cm has 3500 turns of wire wound on a ferromagnetic core of relative permeability 800. What is the magnetic field B in the core for a magnetising current of 1.2 A?

Explanation

`B = (mu_(0) mu_(r) 2"Ni")/(4 pi r)`
` B = (10^(-7) xx 800 xx 2 xx 4000 xx 1.2)/(16 xx 10^(2))`
`B = (8 xx 2 xx 4 xx 1.2)/(16)`
`B = 4.8 T`