A short bar magnet of amgnetic moment 25 `JT^(-1)` is placed with its axis perpendicular to earth the resultant field is inclined at `45^(@)` with earth field if `H=0.4xx10^(-4)`T

Options

A. 5m
B. 0.5 m
C. 2.5 m
D. 0.25 m

Answer

B

Explanation

Since B and H are to each other and resultant field is inclined at an angle `45^(@)` with
so B=H
`therefore (mu_(0))/(4pi)(2M)/(r^(3))=H`
`therefore r^(3)=(mu_(0))/(4pi)(2M)/(H)=0.5 m`