why is spark produced in the switch of a fan ,when it is switched off?

I have answered this in a similar question.

WHEN CURRENT IS SWITCHED OFF, A LARGE INDUCED e.m.f. IS PRODUCED IN THE GAP BETWEEN THE CONTACTS OF THE SWITCH AND THE LIVE WIRE. AS A RESULT OF THIS, A LARGE ELECTRIC FIELD IS PRODUCED WHICH IONISES THE AIR.(CORONA DISCHARGE) THIS ALLOWS THE CURRENT TO PASS THROUGH THE GAP FOR A SHORT INTERVAL OF TIME AND HENCE SPARK IS PRODUCED.

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