Alternating Current

JEE Main level, single correct, medium

114 of 190

Question 114 of 190

The time taken for the magnetic energy to reach 2525% of its maximum value, when a solenoid of resistance RR, inductance LL is connected to a battery, is :

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Answer: (C) LRln2\dfrac{L}{R}ln2

Magnetic energy =12Li2=25=\dfrac{1}{2}L{i}^{2}=25%
ME⇒25ME\Rightarrow 25%\Rightarrow i=\dfrac{{i}_{0}}{2}
i=i0(1−R−Rt/L)i={i}_{0}\left(1-{R}^{-Rt/L}\right) for charging
t=LRln2t=\dfrac{L}{R}ln2

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