JEE Main 2015 · 10 Apr · Shift 1 · Physics Q22

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PhysicsSingle correct+4 / -1Question 22 of 90

In the circuits (a) and (b) switches $S_1$ and $S_2$ are closed at t = 0 and are kept closed for a long time. The variation of currents in the two circuits for t ≥ 0 are roughly shown by (figures are schematic and not drawn to scale) :

(a) A capacitor C and resistor R in series with a cell E and switch S₁. (b) An inductor L and resistor R in series with a cell E and switch S₂.

(a) decays from E/R to zero; (b) rises from zero to E/R

Graph of current i (up to E/R, dashed) against t for circuits (a) and (b): (a) falls from E/R towards zero, (b) rises from zero towards E/R.

(b) decays from E/R to zero; (a) rises from zero to E/R

Graph of current i (up to E/R, dashed) against t for circuits (a) and (b): (b) falls from E/R towards zero, (a) rises from zero towards E/R.

(a) falls, dips and rises again; (b) rises to E/R

Graph of current i (up to E/R, dashed) against t for circuits (a) and (b): (a) falls to a minimum then rises towards E/R; (b) rises towards E/R.

(a) falls from E/R; (b) rises to a peak and then falls

Graph of current i (up to E/R, dashed) against t for circuits (a) and (b): (a) starts at E/R and falls slowly to zero; (b) rises from zero to a peak and falls.

Answer and worked solution

Official answer: A

In the RC circuit (a) the current starts at $\frac ER$ and decays to zero.
In the LR circuit (b) it starts at zero and rises to $\frac ER$ .

That is graph (1).

Topics:RC circuits LR circuits

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JEE Main 2015 · 10 Apr · Shift 1, Physics question 22