A bar magnet is suspended freely in a uniform magnetic field of induction B. When will the rate of change of torque `tau` with deflection `theta ` be maximum? [Here `theta` is the angle between the magnetic field and the magnetic moment of the bar magnet]

Options

A. `theta= 0^(@)`
B. `theta = 45^(@)`
C. `theta = 60^(@)`
D. `theta = 90 ^(@)`

Answer

A

Explanation

`tau = ` MB sin `theta`
`(d tau ) /( d theta )` = MB cos `theta`
For `(d tau )/(d theta ) ` to be maximum
cos `theta = 1 `
`implies theta = 0^(@)`