Capacitors charge and discharge quickly. Charging and discharging depend on the capacitance of the capacitor. In contrast to an inductor which keeps the Current constant, Capacitor keeps the Voltage constant.
How does a capacitor maintain a constant voltage?
Capacitor is made of two conducting plates separated by an insulating Material called “Dielectric”. By placing a voltage source across a capacitor, electrons get accumulated on one of the capacitor plates, and electric field is created. As a result the electrons from the opposite plate are repelled and the plate acquires positive charge.
The other plate is positively charged. Both plates start attracting. Since both plates are separated by an insulating material, the electrons cannot jump onto the other plate. This unrest of the charged plate creates energy. Electrons either dissipate heat or wait until a load is introduced in the circuit.
The circuit below shows a capacitor connected across a battery, the capacitor starts storing energy until the voltage across the capacitor equals the voltage of the Battery.
And a load (LED) is placed across the capacitor. From the below circuit, even when the battery disconnects, the LED continues to glow until the stored energy in the capacitor exhausts. The amount of stored energy in the capacitor is dependent on the Capacitance of the capacitor.
Real world application of this phenomenon?
Capacitors are used in numerous Electronic/Electrical appliances to maintain the voltage even under short period power interruptions/outages.
Amount of charge stored in a capacitor depends on capacitance of a capacitor.
Q (Coulombs)= Capacitance (C) * V (Volts)
Capacitance = (Permittivity of the dielectric material (e) * Area of the capacitor plate(A) ) / (Distance between the Plates(d) )
C=eA/d