If the current through a coil having an inductance of 0.5 H is reduced from 5 A to 2 A in 0.05s, calculate the mean value of the EMF induced in the coil.

Correct option is B

​$$e = L \frac{di}{dt}\textbf{} \\\begin{aligned}& L = \text{Inductance}, \\& di = \text{final value of current - initial value of current}, \\& dt = \text{final time - initial time}.\end{aligned}\textbf{Calculation:} \\\textbf{} \\\begin{aligned}& L = 0.5 \, \text{H}, \\& di = 2 - 5 = -3 \, \text{A}, \\& dt = 0.05 - 0 = 0.05 \, \text{sec}.\end{aligned}\begin{aligned}e &= \frac{L \cdot di}{dt} \\e &= \frac{(0.5) \cdot (-3)}{0.05} \\e &= -30 \, \text{V}.\end{aligned}$$​​