It was observed that an electric current is induced in a coil if there is a flux change in another coil nearby or within the same coil. This is called inductance. Here, the magnetic flux through a coil is directly proportional to the current induced.
That is ΦB α I. And if the geometry of the coil does not change with time, then, dΦBdtα dIdt . For a coil with N turns, N ΦB α I.
Mutual Inductance: If there are two solenoids S1 and S2, with turns N1 and N2 respectively, and a current I2 is set up through S2, then the corresponding flux linkage in S1 can be denoted by
N1 Φ1 = M12 I2
where the constant of proportionality M12, is the mutual inductance of solenoid S1 with respect to solenoid S2 and is also called the coefficient of mutual induction. Its SI unit is Henry (H).
Self-Inductance: It is the phenomenon where emf is induced in a coil due to a change of flux through it by varying the current through itself.
Here, N ΦB α I and N ΦB = L I,
where L is the constant of proportionality and self-inductance of the coil, and it is named the coefficient of self-induction of the coil. Its SI unit is also Henry (H).