Capacitor

Capacitor

A capacitor is a passive two terminal component, which stores electric charge. This component consists of two conductors, which are separated by a dielectric medium. The potential difference when applied across the conductors polarizes the dipole ions to store the charge in the dielectric medium. The circuit symbol of a capacitor is shown below:

The circuit symbol of a capacitor

The circuit symbol of a capacitor

 

The capacitance or the potential storage by the capacitor is measured in Farads, which is symbolized as ‘F’. One Farad is the capacitance when one coulomb of electric charge is stored in the conductor on the application of one-volt potential difference.

The charge stored in a capacitor is given by

Q = CV

Where Q - charge stored by the capacitor

C - Capacitance value of the capacitor

V - Voltage applied across the capacitor

Note the other formula of current, I = d_Q / d_t

Taking the derivative with respect to time,

D_Q/d_t = d(_CV)/d_t

From the above statement, we can express the equation as

I = C (d_V/dt)

As you turn on the power supply, the current begins to flow through the capacitor inducing the positive and negative potentials across its plates. The capacitor continues to charge until the capacitor voltage equalizes up to the supply voltage, which is called as the charging phase of the capacitor. Once the capacitor is fully charged at the end of this phase, it gets open circuited for DC. It begins to discharge when the power of the capacitor is switched off. The charging and discharging of the capacitor is given by a time constant.

 

The voltage across the capacitor is given by

Capacitors are widely used in a variety of applications of electronic circuits such as

·         Store charges such as in a camera flash circuit

·         smoothing the output of power supply circuits

·         coupling of two stages of a circuit (coupling of an audio stage with a loud speaker)

·         Filter networks (tone control of an audio system)