CBSE Class 12 · 2005 · Electromagnetic InductionVery Short Answer

When the current in a coil changes with time, how is the back emf induced in the coil related to it?

Answer: The back emf is proportional to the rate of change of current and opposes it: $e = - L \frac{d I}{d t}$ .

Solution

A changing current changes the flux the coil links with itself, so a self-induced emf appears.
By Faraday's and Lenz's laws this emf opposes the change that produces it, giving

e = - L \frac{d I}{d t}

where

L

is the self-inductance. Thus the back emf is directly proportional to the rate of change of current and is directed so as to oppose that change.

CBSE Class 12 Board · 2005 · Subjective

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