A short bar magnet is placed with its north pole pointing north. The neutral point is `10 cm` away from the centre of the magnet. If `H=0.4G`, calculate the magnetic moment of the magnet.

Options

A. `0.6 A-m^(2)`
B. `0.4Am^(2)`
C. `0.8A-m^(2)`
D. None of the

Answer

B

Explanation

At neutral point `B_(H)=(mu_(0))/(4pi) (M)/(r^(3))`
`rArr M=(B_(H)r^(3))/((mu_(0)//4pi))=((0.4xx10^(-4)) (10xx10^(-2) )^(3))/(10^(-7))`
`=0.4Am^(2)`