A bar magnet of pole strength 2 A-m is kept in a magnetic field of induction `4xx10^(-5) Wbm^(-2)` such that the axis of the magnet makes an angle `30^(@) ` with the direction of the field. The couple acting on the magnet is found to be `80xx10^(-7) N-m.` Then, the distance between the poles of the magnet is

Options

A. 20 cm
B. 2 cm
C. 3 cm
D. 200 cm

Answer

A

Explanation

Torque acting on the magnet `tau=mlB"sin"theta`
`i=(tau)/(mB"sin"theta)`
`implies l=(80xx10^(-7))/(2xx4xx10^(-5)xx"sin"30^(@))`
`therefore l=20xx10^(-2)m=20cm`