The current in a coil of 15 mH increases uniformly from zero to 4 A in 0.004 s . The emf induced in the coil will be :

Calculate the induced emf using the formula: \(\operatorname{emf}=-L \frac{d i}{d t}=-15 \times 10^{-3} \frac{4}{0.004}=-15 \times 10^{-3} \times 1000=\) -15 V . The negative sign indicates the direction of the induced emf, but we are interested in the magnitude, which is 15 V .