Consider a bar magnet having pole strength 2A-m, magnetic length 4cm and area of cros-section `1cm^(2)` Find
(I) the magnetisation I
(II) the magneic intensity H and
(III) the magnetic field at the centre of magnet

Explanation

Given m=2A-m, 2l=4cm,A=1cm^(2)
Magnetisation `I=(M)/(V)=(m.2l)/(A.2l)=(2)/(2xx10^(-4))=2xx10^(4)A//m`
The direction will from S to N-pole
(ii)
At centre, `H_(N)=((mu_(0))/(4pi)(m)/(l^(2)))/(mu_(0))=(m)/(4pil^(2)), "along north pole"` ltbrrgt `H_(S)=(m)/(4pil^(2)), "along south pole"`
`H=H_(N)+H_(S)=(m)/(2pil^(2))=(2)/(2pi(2xx10^(-2))^(2))`
`=(1)/(4pi)xx10^(4)(A)/(m),"along south pole"`
(iii) Magnetic field at the centre of magnet, `B=mu_(0)(H+I)`
`" " 4pixx10^(-7)[-(1)/(4pi)xx10^(4)+2xx10^(4)]`
`" " =-10^(-3)+8pixx10^(-3)=(8pi-1)xx10^(-3)`
`" " =2.4xx10^(-2)T,"along with north pole"`