The force between two magnetic poles is F. If the distance between the poles and pole strengths of each pole are doubled, then the force experienced is :

Options

A. 2 F
B. `F/2`
C. `F/4`
D. F

Answer

D

Explanation

`F = ( mu _(0))/(4pi) . ( 6 M _(1) M _(2))/( r ^(4)) " "...(1)`
When pole strength of each pole becomes double, then magnetic moment of each magnet becomes 4 times that of original magnet.
`therefore F. ( mu _(0))/( 4pi) . ( 6 (4 M _(1)) ( 4 M _(2)))/( (2r) ^(4))= F`