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JEE Main 2019 (11 Jan, Shift 1) · Inductors & DC Transients (Mixed)

Inductors & DC Transients (Mixed) question from JEE Main 2019 (11 Jan, Shift 1)

Q21JEE Main 2019 · 11 JAN · SHIFT 1Difficult

Inductors & DC Transients (Mixed)

In the circuit shown,

Figure

the switch S1 is closed at time t = 0 and the switch S2 is kept open. At some later time(t0), the switch S1 is opened and S2 is closed. The behavior of the current I as a function of time 't' is given by:

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Answer: (a)

  1. S1 closed: the current grows as I=I0(1−e−Rt/L)I = I_0(1 - e^{-Rt/L}), a rising curve.
  2. At t0t_0, S1 opens and S2 closes: L and R form a closed loop, so the current cannot jump; it decays exponentially as I(t0)e−R(t−t0)/LI(t_0)e^{-R(t-t_0)/L}.
  3. Only graph (a) shows a smooth rise followed by an exponential decay (the others decay linearly or rise linearly).
  4. So the answer is (a).
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