MCQ
The back e.m.f. induced in a coil, when current changes from 1 ampere to zero in one milli-second, is 4 volts, the self inductance of the coil is
- A$1 \mathrm{H}$
- B$4 H$
- C$10^{-3} \mathrm{H}$
- ✓$4 \times 10^{-3} \mathrm{H}$
✓
Answer
Correct option: D.
$4 \times 10^{-3} \mathrm{H}$
$e=-L \frac{d i}{d t} \text { but } e=4 V \text { and } \frac{d i}{d t}=\frac{0-1}{10^{-3}}=-1 / 10^{-3}$
$ \therefore \frac{-1}{10^{-3}}(-L)=4 \Rightarrow L=4 \times 10^{-3} \text { henry }$
$ \therefore \frac{-1}{10^{-3}}(-L)=4 \Rightarrow L=4 \times 10^{-3} \text { henry }$
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