What does capacitance measure in a capacitor?

Capacitance measures the ability of a capacitor to store electrical energy per unit voltage applied to it. This property is defined as the ratio of the electric charge stored on one plate of the capacitor to the voltage across the plates. Specifically, capacitance is expressed in farads, and it indicates how much charge the capacitor can hold for a given voltage level.

This is critical for understanding how capacitors function in circuits, as it directly affects their ability to perform tasks such as smoothing voltage fluctuations in power supplies or maintaining power in electronic applications. The other options do not accurately represent the function of capacitance: for instance, while flow of current relates to how charge moves through the circuit, it is not a measure of capacitance itself. Voltage spikes might be related to transient response but not to the fundamental property of capacitance, and voltage rating pertains to the maximum voltage a capacitor can handle without breaking down, not its capacitance.