A2 Daily A Level Physics question
A DC supply of voltage V is connected to a resistor R in series with two identical, initially uncharged capacitors. You can connect the capacitors either in series with each other or in parallel with each other, but in both cases the same resistor R and the same supply V are used. Immediately after the switch is closed, which statement must be true about the current through R?
Answer
The correct answer is A.
Correct: A — The initial current is the same in both cases and equals V/R. At the instant of switching, both arrangements present zero voltage across the uncharged capacitors, so the full supply voltage is across R, giving an initial current of V/R. B is wrong because increasing total capacitance changes how quickly the current falls, not its initial value at the instant of switching. C is wrong because at t = 0+ the series pair still has zero voltage across it; “sharing” of voltage develops later during charging and does not boost the initial current. D is wrong because the initial current is maximum (V/R) and then decreases; it is not zero at first, nor does it rise steadily.