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JEE Main 2014 · 6 Apr · Shift 1, Physics question 21

In the circuit shown here, the point 'C' is kept connected to point 'A' till the current flowing through the circuit becomes constant. Afterward, suddenly, point 'C' is disconnected from point 'A' and connected to point 'B' at time t=0t=0. Ratio of the voltage across resistance and the inductor at t=L/Rt=L/R will be equal to :

A cell, a two-way switch at C (to A, which connects the cell, or to B, which bypasses it), a resistor R and an inductor L in series.
Choose one option
Answer and worked solution

Official answer: C

After switching to B, the cell is out of the circuit and the current decays: i=i0e−Rt/Li=i_0e^{-Rt/L}. Kirchhoff's loop rule gives VR+VL=0V_R+V_L=0 at every instant, so VR/VL=−1V_R/V_L=-1, at t=L/Rt=L/R as at any time.

Topics:LR circuits
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