Consider an air-filled charged capacitor. Which of the following actions will increase its capacitance?$$

A parallel-plate capacitor is charged and then disconnected from the battery. Which of the following changes would halve its capacitance ($C$)?

In a circuit containing a charged $C$ (capacitor) and a switch, what happens to the charge on the $C$ immediately after the switch is thrown to connect the $C$ to a $R$ (resistor)?

In a circuit where a capacitor of capacitance $C$ is discharged through a resistor of resistance $R$, what is the time constant $\tau$ for the discharge process?

In a charged capacitor, where is the energy physically stored?

Which of the following will increase the capacitance $C$ of a parallel-plate capacitor?

Which of the following is a primary function that a capacitor can perform in electrical circuits?

Three capacitors with capacitances $C$, $2C$, and $3C$ are connected in series. What is the equivalent capacitance of the combination?