An average induced emf of 0.50 V appears in a coil when the current in it is changed from 2.5 A in one direction to 2.5 A in the opposite direction in 0.2 s. The self-inductance of the coil would be
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 20 mH
An emf is induced in a coil by its own changing current (self-induction); its average value is the self-inductance times the average rate of change of current.
\( \displaystyle \varepsilon = L\,\frac{\Delta I}{\Delta t} \)
The current reverses direction, so the change is from +2.5 A to −2.5 A:
\( \displaystyle \Delta I = 2.5\,\mathrm{A} - (-2.5\,\mathrm{A}) = 5.0\,\mathrm{A} \)
\( \displaystyle L = \frac{\varepsilon\,\Delta t}{\Delta I} = \frac{0.50\,\mathrm{V} \times 0.2\,\mathrm{s}}{5.0\,\mathrm{A}} \)
\( \displaystyle L = 0.02\,\mathrm{H} = 20\,\mathrm{mH} \)