A magnetic needle suspended parallel to a magnetic field requires 3 ~J of work to turn it through 60^ . The torque needed to maintain the needle in this position will be

Step-by-step solution

In this case, work done aligned W & =M B ( ₁- ₂ ) & =M B ( 0^ - 60^ ) & =M B (1- 1 2 )= M B 2 M B & =2 3 ~J ( given W= 3 ~J ) & =M B 60^ =(2 3 ) ( 3 2 ) J =3 ~J aligned