A short bar magnet is placed along N-S direction with N pole pointing north. The neutral points are located 20 cm away from the bar magnet. If `B_(H)` is the horizontal component of earth's magnetic field then the magnetic field due to the bar magnet at distance of 40 cm along its axis is

Options

A. `(B_(H))/(2)`
B. `(B_(H))/(4)`
C. `(B_(H))/(8)`
D. `(B_(H))/(16)`

Answer

C

Explanation

`B prop (1)/(r^(3))`