What Is a Capacitor?
A capacitor is an essential two-terminal electrical component that stores energy in the form of an electric charge. While it may seem similar to a battery, a capacitor works very differently. Unlike a battery, which converts chemical energy into electrical energy, a capacitor stores electrostatic energy in an electric field.
A capacitor consists of two conductive plates separated by a gap filled with either a vacuum or an insulating material known as a dielectric. The property of storing electrical charge is known as capacitance.
How Does a Capacitor Work?
To understand how a capacitor functions, let’s consider a basic parallel plate capacitor. This setup includes two parallel metal plates separated by a dielectric.
When connected to a DC voltage source, one plate (Plate I) is connected to the positive terminal, and the other (Plate II) to the negative terminal. As voltage is applied:
- Plate I accumulates positive charges.
- Plate II gathers an equal amount of negative charges.
- An electric field forms between the plates.
Since the plates are separated by an insulating material, no current flows through the capacitor in a steady-state DC condition. However, energy is stored in the electric field between the plates.
Charging a Capacitor
As the capacitor charges:
- Positive charges build up on Plate I.
- Negative charges accumulate on Plate II.
- This continues until the voltage across the capacitor equals the supply voltage.
At this point, the capacitor is fully charged, and this duration is referred to as the charging time.
When the power source is removed, the plates retain their charges for a time—making the capacitor act like a temporary energy source.
Discharging a Capacitor
If the capacitor is connected to a load (e.g., a resistor), current flows from Plate I to Plate II through the load. This process continues until all the stored energy is dissipated. This duration is called the discharging time.
How Is Capacitance Determined?
Capacitance CCC is defined as the ratio of the charge QQQ stored on the plates to the voltage VVV across them: C=QVC = \frac{Q}{V}C=VQ
While this formula shows a relationship with charge and voltage, the actual capacitance depends on:
- The surface area of the plates
- The distance between them
- The type of dielectric material used
Capacitors can be either fixed or variable, depending on their application and design.