What is the primary function of a capacitor in a circuit?

The primary function of a capacitor in a circuit is to store and release electrical energy. Capacitors are passive electrical components that accumulate charge when connected to a voltage source. When the voltage source is removed or changed, the stored energy can be released back into the circuit. This ability to store energy makes capacitors invaluable in various applications, such as smoothing out voltage fluctuations in power supplies, filtering signals, and timing applications in oscillators.

The behavior of a capacitor is based on the relationship between its capacitance and the voltage applied across it. When a voltage is applied, the capacitor charges up, and when the circuit demands energy, it discharges, providing the necessary energy to the circuit. This charge and discharge cycle enables capacitors to stabilize voltage and power flow in electronic devices effectively.

In contrast to the other options, capacitors do not actively resist current flow as resistors do, do not convert electrical energy to light (which is the role of devices like light bulbs), and are not used for measuring voltage levels (this function is typically performed by voltmeters). These distinctions highlight the unique and essential role of capacitors in electrical circuits.