The magnetic moment of a bar magnet of geometric length 20 cm is `3.6xx10^(-6) Am^(2)` The magnetic length is 90% of its geometric length the pole strength is

Options

A. `2xx10^(-5)Am`
B. `1.8 xx10^(-4) Am`
C. `7.2 xx10^(-8) Am`
D. `0.55 xx 10^(-4) Am`

Answer

A

Explanation

`2l=(5)/(6)xx"geo.length"`
`(5)/(6)xx20=(100)/(6)cm`
Now" "m`=(M)/(2l)=(3.6xx10^(-6)xx6)/(100xx10^(-2))`
`19.6xx10^(-6)`
`2xx10^(-5)Am`