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 / 2 f R

Following figures show the arrangement of bar magnets in different configurations. Each magnet has magnetic dipole moments m. Which configuration has highest net magnetic dipole moment? 

Two identical long conducting wire AOB and COD are placed at right angle to each other, with one above other such that O is their common point for the two. The wires carry I₁ and I₂ currents, respectively. point P is lying at distance d from O along a direction perpendicular to the plane containing the wires. The magnetic field at the point P will be,

There are four light -weight rod samples A, B, C D separately suspended by threads. A bar magnet is slowly brought near each sample and the following observations are noted
(i)  A is feebly repelled
(ii) B is feebly attracted
(iii) C is strongly attracted
(iv) D remains unaffected

• C is a diamagnetic material

• D is of a ferromagnetic material

• A is of a non- magnetic material

• A is of a non- magnetic material

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

• 2M/π