Answer to Question #266034 in Electricity and Magnetism for Deva

Question

If the back EMF induced in a coil when current changes from 1 ampere to 0 in 1 millisecond, is 5 volts, the self inductance of the coil is:-

(A) 5H

(B) 1H

(C) 5×10^-3 H

(D) 5×10^3 H

Answer 1

The current changes from 1A to 0A.

We know that ;

$e=-L\frac {dP} {dt}$

e=Voltage =e.m.f

L=Inductance

d=change in current

$\frac {dP} {dt} =[\frac {0-1}{\frac {1} {10^2}}] (-L) =5$

$=\frac {L} {10^{-3}}=5$

$=5×10 ^{-3}H$