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JEE Main 2015 (10 Apr, Shift 1) · Inductors & DC Transients (Mixed)

Inductors & DC Transients (Mixed) question from JEE Main 2015 (10 Apr, Shift 1)

Q24JEE Main 2015 · 10 APR · SHIFT 1Medium

Inductors & DC Transients (Mixed)

In the circuits (a) and (b) switches S1 and S2 are closed at t = 0 and are kept closed for a long time. The variation of currents in the two circuits for t ≥\geq 0 are roughly shown by (figures are schematic and not drawn to scale):

Figure

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Answer: (a)

  1. Circuit (a), R-C: the uncharged capacitor acts as a short at t=0t = 0, so i=ERi = \frac{E}{R} at first and then decays as ERe−t/RC\frac{E}{R}e^{-t/RC} to zero.
  2. Circuit (b), L-R: the inductor stops a sudden current, so i=0i = 0 at t=0t = 0 and then grows as ER(1−e−Rt/L)\frac{E}{R}(1 - e^{-Rt/L}) to ER\frac{E}{R}.
  3. So the answer is (a): curve (a) decays from E/RE/R, curve (b) rises to E/RE/R.
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