The same capacitor experiment, two regimes: sort what stays constant when the plate gap is increased.

Groups: Battery stays connected · Battery disconnected

Charge flows back into the source
Charge $Q$ is held fixed
Voltage $V$ is held fixed
Field $E$ between plates is unchanged

Hints

A battery is a voltage clamp; an open circuit is a charge trap.
Whichever quantity is clamped, the others must adjust through $Q = CV$ as $C$ falls.

Show the answer

Battery stays connected: Voltage $V$ is held fixed, Charge flows back into the source

Battery disconnected: Charge $Q$ is held fixed, Field $E$ between plates is unchanged

Why

Connected: $V$ fixed, so $Q = CV$ falls and charge drains to the battery. Disconnected: $Q$ fixed, so $V = Q/C$ rises and $E$ stays put. Identifying "what is held constant" is the key move in every capacitor puzzle.

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The same capacitor experiment, two regimes: sort what stays constant when the plate gap is increased.

Practise Electric Potential and Capacitance

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