A magnet is pointing towards geographic north at a place where horizontal component of earth's magnetic field is `40 mu T ` . Magnetic dipole moment of the bar magnet is `60 Am^(2)` and torque acting on the magnet is `1.2 xx 10^(-3) N` m . What is declination at this place ?

Explanation

`B_(H) = 40 xx 10^(-6) T` .
`tau = 1.2 xx 10^(-3) Nm`
`M = 60 A m^(2)`
`tau = M* B * sin theta`
`1.2 xx 10^(-3) = 60 xx 40 xx 10^(-6) xx sin theta `
`1.2 xx 10^(-3) = 24 xx 10^(-4) xx sin theta`
`1.2 = 2.4 xx sin theta`
`sin theta = (1)/(2)`
`theta = 30^(@)`