How is capacitance defined?

Capacitance is fundamentally defined as the ability of a capacitor to store an electric charge. It is quantified as the amount of electric charge (measured in coulombs) that can be stored per unit voltage (measured in volts). Therefore, if we consider the relationship between charge and voltage, capacitance can be expressed mathematically as C = Q/V, where C is the capacitance, Q is the charge stored, and V is the voltage across the capacitor.

In this context, option A accurately describes capacitance, as it addresses the amount of charge a capacitor can store, which is a direct reflection of its capacitance. However, capacitance is inherently tied to how that stored charge relates to voltage.

The other options don't accurately capture the essence of capacitance. Option C pertains to the condition of the capacitor when it is fully charged, not the definition of capacitance itself. Option D discusses the current flowing through a capacitor, which is related to the capacitor’s behavior in a circuit but does not define capacitance.

In summary, capacitance is defined by the relationship of stored charge to voltage, emphasizing how it encapsulates the ability of a capacitor to hold charge in response to a given voltage.