What happens to the current in an RC circuit as a capacitor charges toward its supply voltage?

• A. The current decays exponentially toward zero.
• B. The current increases linearly.
• C. The current remains constant.
• D. The current oscillates.

Answer: (A)

In an RC charging circuit, the current fades as the capacitor voltage climbs toward the supply value. The loop gives V = iR + vC and i = C dvC/dt. Solving these together shows i(t) = (V/R) e^{-t/RC}. So the current starts at V/R and decays exponentially toward zero as the capacitor charges. The rate is set by the time constant RC. There’s no oscillation or constant current in this simple, non-inductive circuit, and the current decreases because the voltage across the resistor drops as the capacitor voltage rises.