Question

In series with 20 ohm resistor a 5 henry inductor is placed. To the combination an e.m.f. of 5 volt is applied. What will be the rate of increase of current at t = 0.25 sec

• A. e
• B. e^–2
• C. e^–1
• D. None of these

Answer 1

The correct option is C e^–1

$i=i_o(1-e^{-\frac{Rt}{L}})\Rightarrow \frac{di}{dt}=i_o\left(\frac{R}{L}\right)e^{\frac{Rt}{L}}=\frac{E}{L}{e}^{\frac{Rt}{L}}$
On putting values $\frac{di}{dt}=\frac{1}{e}=e^{-1}.$