A particle of charge q moving with a speed v on entering a magnetic field B, experiences magnetic Lorentz force which acts as a centripetal force.

here, is the cyclotron frequency.

Both Biot- Savart’s lawand ampere’s circuital lawdeal with the consequences of steady current. Ampere’s circuital law is to Biot- savart’s law as is Gauss’s law to Coulomb’s law in electrostatics.

the expression for Ampere’s circuital law is where I is the current included in the surface bounded by the line integral.

The magnetic field at the centre of a solenoid with air core is .where,is the permeability of free space, n the number of turns per unit length and I is the current flowing through the solenoid.

A toroid is a solenoid wound on itself. The magnetic field exists only in the region of the hollow circular ring which has the turns of wire wound on it. Using Ampere’s circuital law,

The conductor carrying current Ib is placed in the magnetic field created by the conductor carrying current . The force it experiences

The torque experienced by a current carrying conductor placed in a magnetic field is given by .This has a maximum value when;

The torque experienced by a current carrying coil of N turns placed in a magnetic field.For N =1, Comparing with torque experienced by a electric dipole

The electron moving in a circular orbit of radius r with a speed v and time period T constitutes a current .since,thereforeThe orbital magnetic moment of the electron The angular momentum of the electron ,sincetherefore,

In a moving coil galvanometer, the coil is pivoted on a helical spring. When current passes through the coil, it experiences a torque and deflects. A restoring torque is set up in the helical spring which tries to restore the coil to its original position.