A toroid has an iron core with an internal magnetic field of `10 pi mT`, when the current in the winding of 1500 turns per meter is 10 A. Determing the field due to magnetisation `(mu = 4pi xx 10^(-7) Hm ^(-1))`

Options

A. `(4 pi) mT`
B. `(10 pi) mT`
C. ` (8/pi) mT`
D. `(pi/4) mT`

Answer

A

Explanation

Given internal magnetic field ` B_(net) = 10 pi mT` current flowing through winding I = 10 A and number of turns per unit legth n= 1500 since magnetic field of toroid,
`B_("toroid") = mu _0 nI`
`= 4pi xx 10^(-7) xx 1500 xx 10 = 6pi mT`
Hence the filed due to magnetisation
`B_m = B_(net) - B _("toroid") = 10 pi - 6pi`
`rArr B_m = 4pi mT`