Describe how back EMF was induced in self induction ?

Back EMF is induced in self-induction when the current flowing through a coil of wire changes. When the current in the coil is increasing, the magnetic field around the coil also increases. This changing magnetic field induces an electromotive force (EMF) in the coil that opposes the change in current. This opposing EMF is known as back EMF.

The back EMF is proportional to the rate of change of current in the coil, as described by Faraday's law of electromagnetic induction. The back EMF acts to oppose the change in current, which can lead to effects such as voltage spikes or voltage drops in the circuit.

In self-induction, the coil of wire is both the source of the changing magnetic field and the conductor through which the induced EMF flows. This can occur in devices such as solenoids, transformers, or inductors, where the changing current in the coil induces a back EMF that affects the behavior of the circuit.