Question

A bar magnet of length 0.1m has pole strength of 50A-m. Calculate the magnetic field at distance of 0.2m from tis centre on
(i) its axial line and (ii) it equatorial line.

Answer 1

Here, m=50A-m, r=0.2m, 2l=0.1m or l=0.05m
Magnetic dipole moment,
`" " M=m(2l)=50xx0.1=5A-m^(2)`
`(i) B_("axial")=(mu_(0))/(4pi) (2Mr)/((r^(2)-l^(2)))=(10^(-7)xx2xx5xx0.2)/((0.2^(2)-0.05^(2))^(2))=1.42xx10^(-4)T`
`(i) B_("equi")=(mu_(0))/(4pi) (2Mr)/((r^(2)+l^(2)))=(10^(-7)xx5)/((0.2^(2)-0.05^(2))^(2))`
Formula with `(r^(2)-l^(2)) and (sigma^(2)rhol^(2))` are used become here `r gt gt l` does not apply.