The magnetic induction at a distance `'d'` form the magnetic pole of unkown strength `'m'` is `B`. If an identical pole is now placed at a distance of `2d` from the first pole, the force between the two poles is

Options

A. `mB`
B. `(mB)/(2)`
C. `(mB)/(4)`
D. `2mB`

Answer

C

Explanation

`B=(mu_(0))/(4pi)(m)/(d^(2))` and
`F=(mu_(0))/(4pi)(mm)/((2d)^(2))=(mu_(0))/(4pi)(m)/(d^(2))xx(m)/(4)=(Bm)/(4)`