# Physics Class 12 NCERT Solutions: Chapter 4 Moving Charges and Magnetism Part 2

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Q: 6. A wire carrying a current of is placed inside a solenoid perpendicular to its axis. The magnetic field inside the solenoid is given to be. What is the magnetic force on the wire?

Length of the wire,

Current flowing in the wire,

Magnetic field,

Angle between the current and magnetic field,

Magnetic force exerted on the wire is given as:

Hence, the magnetic force on the wire is. The direction of the force can be obtained from Fleming’s left hand rule.

Q: 7. Two long and parallel straight wires A and B carrying currents of and in the same direction are separated by a distance of 4.0 cm. Estimate the force on a 10 cm section of wire A.

Current flowing in wire

Current flowing in wire

Distance between the two wires,

Length of a section of wire

Force exerted on length l due to the magnetic field is given as:

Where,

Permeability of free space

The magnitude of force is . This is an attractive force normal to A towards B because the direction of the currents in the wires is the same.

Q: 8. A closely wound solenoid long has layers of windings of turns each. The diameter of the solenoid is. If the current carried is, estimate the magnitude of B inside the solenoid near its centre.

Length of the solenoid,

There are five layers of windings of turns each on the solenoid.

Total number of turns on the solenoid,

Diameter of the solenoid,

Current carried by the solenoid,

Magnitude of the magnetic field inside the solenoid near its centre is given by the relation,

Where,

Permeability of free space

Hence, the magnitude of the magnetic field inside the solenoid near its centre is

Q: 9. A square coil of side consists of turns and carries a current of. The coil is suspended vertically and the normal to the plane of the coil makes an angle of with the direction of a uniform horizontal magnetic field of magnitude. What is the magnitude of torque experienced by the coil?

Length of a side of the square coil,

Current flowing in the coil,

Number of turns on the coil,

Angle made by the plane of the coil with magnetic field,

Strength of magnetic field,

Magnitude of the magnetic torque experienced by the coil in the magnetic field is given by the relation,

Where,

A = Area of the square coil

Hence, the magnitude of the torque experienced by the coil is.

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