Capacitors and Capacitance - SS2 Physics Lesson Note

Capacitors are electronic components that store electric charge and energy in an electric field. They are widely used in electronic circuits and have numerous applications.

Capacitance:

Capacitance is a property of capacitors that measures their ability to store electric charge. It is denoted by the symbol C and is measured in farads (F). Capacitance is defined as the ratio of the magnitude of the electric charge on one of the capacitor plates to the electric potential difference (voltage) between the plates. Mathematically, C = Q/V, where Q is the charge and V is the voltage. The capacitance of a capacitor depends on its physical characteristics, such as the size, shape, and spacing of the plates, as well as the type of dielectric material between the plates. The capacitance of a capacitor is typically specified on the component itself and determines its ability to store charge and energy.

Capacitor Construction:

Capacitors consist of two conductive plates separated by a dielectric material. The conductive plates are usually made of metal, such as aluminium or tantalum. The dielectric material between the plates serves to insulate them and prevent direct electrical contact. It can be made of various materials, such as ceramic, plastic, or electrolyte. The physical structure of capacitors can vary, including configurations such as parallel plate capacitors, cylindrical capacitors, and electrolytic capacitors.

Charging and Discharging of Capacitors:

When a voltage is applied across the terminals of a capacitor, it charges up by accumulating an equal amount of positive and negative charges on its plates. During the charging process, the capacitor stores electric potential energy in the electric field between the plates. The charging time depends on the capacitance of the capacitor and the resistance in the circuit. When the voltage source is removed, the capacitor can discharge its stored energy through a circuit. The discharge time depends on the capacitance and the resistance in the circuit.

Energy Storage and Capacitor Formulae:

Capacitors store energy in the form of electric potential energy. The energy stored in a capacitor is given by the formula U = (1/2)CV2, where U is the energy, C is the capacitance, and V is the voltage. The amount of charge stored in a capacitor is given by the formula Q = CV, where Q is the charge and V is the voltage. The time taken for a capacitor to charge or discharge to a certain percentage of its final value is determined by the time constant, τ = RC, where R is the resistance and C is the capacitance.

Capacitors in Circuits:

Capacitors are used in various electronic circuits for different purposes. They can be used as energy storage devices, timing elements, filters, and coupling or decoupling components. In AC (alternating current) circuits, capacitors are used in combination with resistors and inductors to form filters and timing circuits. Capacitors can also be used in power factor correction circuits, voltage regulation circuits, and as memory elements in electronic devices.

Capacitors and capacitance are essential components in electronic circuits, allowing for the storage and controlled release of electrical charge and energy. They find applications in a wide range of devices, from simple electronic circuits to advanced electronic systems. Understanding capacitors and capacitance is fundamental for anyone working in the field of electronics.