A 250-Turn rectangular coil of length 2.1 cm and width 1.25 cm carries a current of 85 μA and subjected to a magnetic field of strength 0.85 T. Work done for rotating the coil by 180° against the torque is

• 9.1 μJ

• 4.55 μJ

• 2.3 μJ

• 1.15 μJ

A bar magnet of length l and magnetic dipole moment M is bent in the form of an arc as shown in figure, The new magnetic dipole moment will be

• M

• 3M/π

• 2M/π

• M/2

A compass needle which is allowed to move in a horizontal plane is taken to a geomagnetic pole. it

• will become rigid showing no movement

• will stay in any position

• will stay in the north-south direction only

• will stay in the east-west direction only

A rectangular, a square a circular and an elliptical loop, all in the (x-y) plane, are moving out of a uniform magnetic field with a constant velocity, The magnetic field is directed along the negative z- axis direction. The induced emf, during the passage of these loops, out the field region, will not remain constant for

• the rectangular, circular and elliptical loops

• the circular and the elliptical loops

• only the elliptical loops

• any of the four loops

A thin ring of radius R metre has charge q column uniformly spread on it. The ring rotates about its axis with a constant frequency of  f revolution/s. The value of magnetic induction in Wb m^-2 at the centre of the ring is

• μ_oq f/ 2π R

• μ_oq / f 2π R

• μ_oq / 2 f R

• μ_oq f / 2 R