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Charging and Discharging of Capacitor and Capacitance

by Gerua Senia

What is a Capacitor?

The device which is used to store energy is called Capacitor. The function of the capacitor is to store electrical energy and give out this energy when it is necessary. It is an electronic component with two terminals. The main application of the capacitor is charging and discharging of electric charges. It can be also used to block DC current and pass AC current. It is used as sensors to measure air humidity, fuel levels etc. The capacitors are used to protect sensitive devices. It consists of two conductors kept close to each other and it is separated by an insulator. Capacitors are of different types. Few types of capacitors are aluminium electrolyte capacitor, ceramic capacitors, tantalum and niobium capacitors.

What is Capacitance?  

The effect of the capacitor is called capacitance. It is the amount of electric charge that can be stored in the capacitor per unit change in the electric potential. If an electric charge is transferred between two uncharged conductors they get equally charged. One of the conductors gets positively charged and the other gets charged negatively This creates a potential difference between them. 

The capacitance (C ) is the ratio of the amount of charge (q) in one of the conductors and the potential difference between the conductors. We can write it as

C = q/V . The SI unit of capacitance is Farad. The capacitance can be increased by connecting the capacitors in parallel and it can be decreased by connecting the capacitors in series.

Charging and Discharging of Capacitor

The charging of capacitor means filling the capacitor with a certain amount of energy. Discharging the capacitor is to drain or remove the stored energy in the capacitor. Charging and discharging of a capacitor is a way of adding and subtracting energy charge.

Knowing the rate at which charging and discharging happen in the capacitor makes it a useful device in electronic circuits. The rate at which capacitor charges or discharges depends on the capacitance of the capacitor and the resistance of the circuit. During charging electrons from the negative terminal of the battery flows to one conductor plate of the capacitor and from the other plate to the positive terminal of the battery. The flow of electrons will not continue indefinitely. 

The flow of electrons ceases when the potential difference between the plates becomes equal to the potential of the battery. Adding a resistor in series to the circuit only reduces the time it takes for the capacitor to charge and not the eventual potential difference.

When the capacitor is discharged a large charge starts to flow and the and the potential difference across the capacitor drops. As the charge continues to flow from one plate of the capacitor to the other through the resistor the charge will be neutralized which causes the current to reduce and the potential difference also decreases. Eventually the current and the potential difference becomes zero. The capacitor is fully discharged.



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