Electro Magnetic Induction And Alternating Currents Question 597
Question: The resistance and inductance of series circuit are $ 5\Omega $ and 20H respectively. At the instant of closing the switch, the current is increasing at the rate 4A-s. The supply voltage is [MP PMT 2004]
Options:
A) 20 V
B) 80 V
C) 120 V
D) 100 V
Show Answer
Answer:
Correct Answer: B
Solution:
$ i=i_{0}( 1-{{e}^{-\frac{Rt}{L}}} ) $
$ \Rightarrow \frac{di}{dt}=-i_{0}( -\frac{R}{L} ){{e}^{-\frac{Rt}{L}}}=\frac{i_{0}R}{L}.{{e}^{-\frac{Rt}{L}}} $
At t = 0 ; $ \frac{di}{dt}=\frac{i_{0}R}{L}=\frac{E}{L} $
$ \Rightarrow 4=\frac{E}{20}\Rightarrow E=80\ V $
