A long wire carrying a steady current is bent into a circular loop of one turn. The magnetic field at the centre of the loop is B. It is then bent into a circular coil of n turns. What will the magnetic field be at the centre of this n-turn coil?

1.	nB	2.	n2B
3.	2nB	4.	2n2B

If an i-ampere current flows through an infinitely long, straight, thin-walled tube, what will be the magnetic induction at any point within the tube?

If the magnetic field at the centre of the circular coil is B₀, then what is the distance on its axis from the centre of the coil where  \(B_x=\frac{B_0}{8}~?\)
(R= radius of the coil)

A charged particle is projected in a uniform magnetic field at an angle of 45° to the magnetic field. If the circumference of the helical path followed by it is 2 cm, then the pitch of the helix will be:

1. 1 cm

2. \(\sqrt{2}\) cm

3. 2 cm

4. 4 cm

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.