A wire of length l carrying current i is folded to form a circular coil of N turns. What should be the value of N to have the maximum value of the magnetic moment in the coil?

1. 1

2. 4

3. 9

4. 10

If charge -Q is moving vertically upwards, then what will be the force on the charged particle if it enters a magnetic field that is pointed towards the south?

1. North

2. South

3. East

4. West

What happens when the number of turns in a galvanometer is doubled?

The two parts of the loop are circles of radii 2a and a, respectively, and carry the same current i as shown in the given figure. What is the magnitude of the dipole moment of the current loop?

1. $5{\mathrm{\pi a}}^2$ $\mathrm{i}$

2. $4{\mathrm{\pi a}}^2$ $\mathrm{i}$

3. $3{\mathrm{\pi a}}^2$ $\mathrm{i}$

4. Zero

What is the magnetic moment of the following current loop?
 
1. $24$ $A{m}^2$

2. $12$ $A{m}^2$

3. $6$ $A{m}^2$

4. Zero

An electron and a proton are revolving around a common centre O in two coplanar circular paths as shown in the figure with a time period of rotation of 1 s and 2 s, respectively. What will be the net magnetic field at O?

1. \(\frac{\mu _{0}e}{\pi }\) tesla.
2. \(\frac{\mu _{0}e}{2}\) tesla.
3. \(2\mu _{0}e\) tesla.
4. zero.

As indicated, a long, straight conductor XY carrying a current i₁ is placed antiparallel to a conductor AB of length l carrying a current i₂. How much of a force is acting on AB?

1. ${\mu }_0{i}_1{i}_2$

2.  $\frac{{\mu }_0{i}_1{i}_2}{\mathrm{\pi }}$

3. $\frac{{\mu }_0{i}_1{i}_2}{2\mathrm{\pi }}$

4. $2{\mu }_0{i}_1{i}_2$

If a long hollow copper pipe carries a direct current along its length, then the magnetic field associated with the current will be:

Magnetic field at the outer surface of long hollow cylindrical shells of radius R and carrying current I is B. What is the magnetic field at a distance of $\frac{3R}{2}$ from the axis of the cylindrical shell?

On connecting a shunt of \(10 ~ \Omega,\) the deflection in a moving coil galvanometer falls from 40 divisions to 6 divisions. What is the resistance of the galvanometer?