A bar magnet is held at right angle to a uniform magneitc field. The couple acting on the acting on the magnet is to be halved by rotating it form this position. The angle of rotation is

Options

A. `60^(@)`
B. `45^(@)`
C. `30^(@)`
D. `75^(@)`

Answer

A

Explanation

As `, tau=MB sin theta `
where , ` theta =90^(@) implies tau =MB`
Given , ` tau_(2)=(1)/(2) tau_(2) implies MB sin theta =(1)/(2) MB`
`implies sin theta =(1)/(2) implies theta =30^(@)`
`:. ` Angle of rotation `=90^(@)- 30^@ =60^(@)`