Capacitors and Capacitance - SS2 Physics Lesson Note
Capacitors and capacitance are fundamental components in electrical circuits that store and release electrical energy. They are widely used in various electronic devices and systems.
Capacitors:
A capacitor is a two-terminal electronic component that stores electrical energy in an electric field. It consists of two conductive plates separated by an insulating material called a dielectric. When a voltage is applied across the plates, opposite charges accumulate on the plates, creating an electric field between them. The capacitor can store electrical energy in this electric field.
Capacitance:
Capacitance is a property of a capacitor that measures its ability to store electrical charge. It is defined as the ratio of the electric charge stored on each plate of the capacitor to the voltage applied across the plates. Mathematically, capacitance is given by the equation:
C = Q/V
where C is the capacitance, Q is the charge stored on the plates, and V is the voltage applied across the plates. The unit of capacitance is the Farad (F).
Types of Capacitors:
There are various types of capacitors available, including:
1. Ceramic Capacitors: These capacitors use a ceramic material as the dielectric and are commonly used in electronic circuits due to their small size and stability.
2. Electrolytic Capacitors: Electrolytic capacitors have a higher capacitance value and are polarised, meaning they have positive and negative terminals. They are often used in power supply circuits.
3. Film Capacitors: Film capacitors use a thin plastic film as the dielectric and can have a wide range of capacitance values. They are used in a variety of applications, including audio and radio frequency circuits.
Capacitor Charging and Discharging:
When a capacitor is connected to a voltage source, such as a battery, it charges up by accumulating charges on its plates. The time it takes for a capacitor to charge or discharge depends on its capacitance and the resistance in the circuit. This behaviour can be described by the RC time constant, where R is the resistance and C is the capacitance.
Energy Storage and Release:
Capacitors store electrical energy in their electric fields. The energy stored in a capacitor is given by the equation:
E = (1/2)CV2
where E is the energy, C is the capacitance, and V is the voltage across the plates. When the capacitor is discharged, it releases the stored energy back into the circuit.
Applications of Capacitors:
Capacitors have various applications in electrical and electronic systems, including:
1. Energy Storage: Capacitors are used to store electrical energy in applications such as power backup systems and camera flashes.
2. Timing and Filtering: Capacitors are used in timing circuits and filters to control the flow of electrical signals.
3. Coupling and Decoupling: Capacitors are used to couple and decouple signals in electronic circuits, allowing the transmission of desired signals while blocking unwanted signals.
4. Power Factor Correction: Capacitors are used to improve the power factor in electrical systems, leading to efficient power transmission.
Capacitors are essential components in electronic circuits and play a crucial role in energy storage, signal processing, and power management. Understanding capacitance and the behaviour of capacitors is fundamental in designing and analysing electrical systems and circuits.