alleryStart learning →In an RC charging circuit, when is the current largest?
AAt the moment the capacitor is fully charged
BAt the instant the switch is first closed
CAfter exactly one time constant has passed
DIt stays the same throughout the charging
Answer & Solution
Correct answer: B. At the instant the switch is first closed
1. At the instant of closing, the capacitor is uncharged and holds no voltage of its own.
2. The whole emf then appears across the resistance, giving the largest current the circuit can have.
3. As charge builds up, the capacitor voltage opposes the battery and the current falls away.
4. When the capacitor voltage has grown to match the emf, the current has fallen to zero.
5. So the current is at its peak first and decays, never staying constant through the charging.
_Source: OpenStax College Physics (CC BY 4.0), Ch 21 "Circuits and DC Instruments", section 21.6 DC Circuits Containing Resistors and Capacitors_
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