Inductance

A small coil is introduced between the poles of an electromagnet so that its axis coincides with the magnetic field direction. The number of turns is n and the cross-sectional area of the coil is . When the coil turns through about its diameter, the charge flowing through the coil is . The total resistance of the circuit is . What is the magnitude of the magnetic induction?

A solenoid has turns wound over a length of . The area of its cross-section is . Around its central section, a coil of turn is wound. If an initial current of in the solenoid is reversed in , then the emf induced in the coil is

A square current carrying loop is changed to a circular loop in time . Then

For a current carrying inductor, emf associated is 20mV. Now, current through it changes from 6A to 2A in 2s. The coefficient of mutual inductance is