A circular coil of wire consisting of 100 turns, each of radius 8.0 cm carries a current of 0.40 A. What is the magnitude of the magnetic field B at the centre of the coil?

1.\(3.14 \times 10^{-4} \ T\) 
2.\(2.12 \times 10^{-4} \ T\) 
3.\(1.41 \times 10^{-4} \ T\) 
4.\(2.01 \times 10^{-4} \ T\)
 

Two moving coil meters, M₁ and M₂ have the following particulars: 

R₁ = 10 Ω, N₁ = 30, A₁ = 3.6 x 10^-3 m² and B₁ = 0.25 T

R₂ = 14 Ω, N₂ = 42, A₂ = 1.8 x 10^-3 m² and B₂ = 0.50 T

( The spring constants are identical for the two meters.)
The ratio of current sensitivity (M₂ to M₁) is: 

 

A square coil of side \(10~\text{cm}\) consists of \(20~\text{turns}\) and carries a current of \(12~\text{A}\). The coil is suspended vertically and the normal to the plane of the coil makes an angle of \(30^{\circ}\) with the direction of a uniform horizontal magnetic field of magnitude \(0.80~\text{T}\). What is the magnitude of torque experienced by the coil?
1. \(0.79~\text{N-m}\)
2. \(0.88~\text{N-m}\)
3. \(0.49~\text{N-m}\)
4. \(0.96~\text{N-m}\)

Closely wound solenoid 80 cm long has 5 layers of windings of 400 turns each. The diameter of the solenoid is 1.8 cm. If the current carried is 8.0 A, the magnitude of B inside the solenoid near its centre is:

1.\(3.7 \times 10^{-2} \ T\)
2.\(3.1 \times 10^{-2} \ T\)
3.\(2.5 \times 10^{-2} \ T\)
4.\(1.44 \times 10^{-2} \ T\)

Two long and parallel straight wires A and B carrying currents of \(8.0\) A and \(5.0\) A in the same direction are separated by a distance of \(4.0\) cm. The force on a \(10\) cm section of wire A is:
1. \(3\times10^{-5}\) N
2. \(2\times10^{-5}\) N
3. \(3\times10^{-4}\) N
4. \(2\times10^{-4}\) N

A 3.0 cm wire carrying a current of 10 A is placed inside a solenoid perpendicular to its axis. The magnetic field inside the solenoid is given to be 0.27 T. What is the magnetic force on the wire?

1.\(8.1 \times 10^{-2} \ N\)
2.\(9.8 \times 10^{-2} \ N\)
3. \(7.6 \times 10^{-2} \ N\)
4.\(6.8 \times 10^{-2} \ N\)

What is the magnitude of magnetic force per unit length on a wire carrying a current of \(8~\text{A}\) and making an angle of \(30^{\circ}\) with the direction of a uniform magnetic field of \(0.15~\text{T}\)?

A horizontal overhead power line carries a current of \(90\) A in the east to west direction. What is the magnitude and direction of the magnetic field due to the current \(1.5\) m below the line?
1. \(1.2 \times 10^{-5}\) T, towards north
2.  \(2.1 \times 10^{-5}\) T, towards south
3.  \(1.2 \times 10^{-5}\) T, towards south
4.  \(2.1 \times 10^{-5}\) T, towards north

A long straight wire in the horizontal plane carries a current of 50 A in the north to south direction. The magnitude and direction of the magnetic field at a point 2.5 m east of the wire is:
1. \(4 \times 10^{-6}~ T\) vertically upward
2. \(4 \times 10^{-6} ~T\) vertically downward
3. \(3 \times 10^{-6} ~T\) vertically upward
4. \(3 \times 10^{-6} ~T\) vertically downward

A long straight wire carries a current of \(35\) A. The magnitude of the magnetic field at a point \(20\) cm from the wire is:
1. \(3.5 \times 10^{-6} \) T
2. \(3.5 \times 10^{-5} \) T
3. \(4.5 \times 10^{-6} \) T
4.\(4.5 \times 10^{-5} \) T