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 $\frac{di}{dt}=\frac{1}{e}=e^{-1}.$