Two insulated rings, one of a slightly smaller diameter than the other, are suspended along their common diameter as shown. Initially, the planes of the rings are mutually perpendicular. What happens when a steady current is set up in each of them?

 

1.	the two rings rotate into a common plane.
2.	the inner ring oscillates about its initial position.
3.	the inner ring stays stationary while the outer one moves into the plane of the inner ring.
4.	the outer ring stays stationary while the inner one moves into the plane of the outer ring.

A charge Q is uniformly distributed on a ring of radius R made of an insulating material. If the ring rotates about the axis passing through its centre and normal to the plane of the ring with constant angular speed ω, then what will be the magnitude of the magnetic moment of the ring?

1. $Q\omega R^2$
2. $\frac{1}{2}Q\omega R^2$
3. $Q{\omega }^{2}R$
4. $\frac{1}{2}Q{\omega }^{2}R$

What is the net force on the square coil ?

(1) $25\times {10}^{-7}N$ moving towards wire

(2) $25\times {10}^{-7}N$ moving away from wire

(3) $35\times {10}^{-7}N$ moving towards wire

(4) $35\times {10}^{-7}N$ moving away from wire

Two long parallel copper wires carry currents of 5 A each in opposite directions. If the wires are separated by a distance of 0.5 m, then the force between the two wires will be:

What is the relation between voltage sensitivity (σ_v) and current sensitivity (σ_i) of a moving coil galvanometer? (Resistance of Galvanometer = G)

1. $\frac{{\sigma }_i}{G}={\sigma }_v$                           

2. $\frac{{\sigma }_v}{G}={\sigma }_i$

3. $\frac{G}{{\sigma }_v}={\sigma }_i$                           

4. $\frac{G}{{\sigma }_i}={\sigma }_v$

Two galvanometers A and B require 3mA and 5mA respectively to produce the same deflection of 10 divisions. Then

(1) A is more sensitive than B

(2) B is more sensitive than A

(3) A and B are equally sensitive

(4) Sensitiveness of B is 5/3 times that of A

There long straight wires A, B and C are carrying current as shown figure. Then the resultant force on B is directed 

(1) Towards A

(2) Towards C

(3) Perpendicular to the plane of paper and outward

(4) Perpendicular to the plane of paper and inward

Two long conductors, separated by a distance d carry current $I_1$ and $I_2$ in the same direction. They exert a force F on each other. Now the current in one of them is increased to two times and its direction is reversed. The distance is also increased to $3d$. The new value of the force between them is-

1. $-2F$                           

2.  $2F/3$

3. $-2F/3$                           

4. $-F/3$

Current i is carried in a wire of length L. If the wire is turned into a circular coil, the maximum magnitude of torque in a given magnetic field B will be:

1. $\frac{Li{B}^2}{2}$                     2. $\frac{L{i}^{2}B}{2}$

3. $\frac{L^{2}iB}{4\mathrm{\pi }}$                     4. $\frac{L{i}^{2}B}{4\mathrm{\pi }}$

An arrangement of three parallel straight wires placed perpendicular to the plane of paper carrying the same current I along the same direction as shown in the figure. Magnitude of force per unit length on the middle wire B is given by:

1. $\frac{{\mu }_o{i}^2}{2\mathrm{\pi d}}$

2. $\frac{2{\mu }_0{i}^2}{\mathrm{\pi d}}$

3. $\frac{\sqrt{2}{\mu }_o{i}^2}{\pi d}$

4. $\frac{{\mu }_o{i}^2}{\sqrt{2}\mathrm{\pi d}}$