A) 4 s
B) 3 s
C) 2 s
D) 1 s
Correct Answer: C
Solution :
| Key Idea: The emf is given by the relation \[e=-L\frac{dt}{dt}\]. |
| It is given that emf is zero i.e., |
| \[e=-L\,\frac{di}{dt}=0\] |
| or \[L\,\frac{di}{dt}=0\] |
| or \[\frac{d}{dt}({{t}^{2}}{{e}^{-t}})=0\] |
| or \[2t\times {{e}^{-t}}+{{t}^{2}}+(-1)\,{{e}^{-t}}=0\] |
| or \[t{{e}^{-t}}(2-t)=0\] |
| or \[t=2\,s\] \[(\because \,t{{e}^{-t}}\ne 0)\] |
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