how is emf induced in a current carrying coil

When EMF is induced in the coil due to its own current, it is called Self induction. It happens only if the magnetic field through the coil is changing somehow with time and hence, there is a change in magnetic flux through the coil. Therefore, whenever we switch off the light, the current in the circuit starts decreasing and hence EMF is induced according to lenz's law such that the current is supported and hence sometimes we see spark in the switch.
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Apoorva Arora
IIT Rorrkee
askIITians Faculty