A magnetised needle of magnetic moment `4*8xx10^-2JT^-1` is placed at `30^@` with the direction of uniform magnetic field of magnitude `3xx10^-2T`. What is the torque acting on the needle?

Options

A. `7.2 xx 10^(-1) N-m`
B. `7.2 xx 10^(-2) N-m`
C. `7.2 xx 10^(-4) N-m`
D. `7.2 xx 10^(-3) N-m`

Answer

C

Explanation

Here, `M = 4.8 xx 10^(-2) Am^(2)`
`theta = 30^(@), B = 3 xx 10^(-2) T`
`= MB sin theta`
`= 4.5 xx 10^(-2) xx 3 xx 10^(-2) sin 30^(@)`
`= 7.2 xx 10^(-4) Nm`