The Action of a Capacitor

Capacitor is a device which is used for the storage of charges consisting of two conductors, parallel-nearly separated by air or any other dielectric.Dielectric is an insulating medium used between plates of a capacitor.

Mode of Action of a Capacitance

Explain mode of action of a capacitance

The capacitor store energy by keeping electrical charges on its plates. Capacitors are used in radio circuits, television circuits and other electronic devices.

When the power switches off, the energy stored in the plates of the capacitor will be released to flow in the circuit for sometimes. This will keep the device functioning until all the energy is worn out.

That means, when the electric power is available, the capacitor is charged and store electric energy on its plates but when the power in the circuit switches OFF, the capacitor continues to supply the electrical power in the circuit. This process through which the capacitor releases its charges to the circuit is known as discharging.

The Action of a Capacitor

Explain the action of a capacitor

A fully charged capacitor has a net positive charge on one of its plates and a net negative charge on the other plate. The potential difference between its plates can be measured by connecting the voltmeter across its plates.

The ability of a capacitor to store charges is known as the capacitance. Capacitance is the ratio between the quantity of charge stored and the potential difference (p.d) across the plates of the capacitor.

That means, the quantity of charges Q increases with the increase in the potential difference (p.d) across the plates.

The S.I unit of capacitance is is Farads (F). Other units include microfarads (µF), picofarads (Pf) and nanoFarads (nF).

A farad is the capacitance of a conductor that its potential difference can be changed by 1 volt by a charge of 1 coulomb.

However, 1 Farad capacitance is very large to be reached thus most of the times the smaller units are used to simplify measurements.

Example 1

A 3µF capacitor has a 18V of potential difference. What will be its total charge?

Example 2

Calculate the capacitance of the capacitor if the cell connected to it has 1.5V when the charge is 120 coulombs.

Construction of an Air-filled Capacitor

Describe the construction of an air-filled capacitor

This constitute two parallel metal plates with air band between them.A flat metal A is set up vertically on insulating legs and is connected to a gold leaf electroscope by means of a wire.

The plate is then given a positive charge by induction with a negatively charged ebonite rod. The divergence of the leaf indicates the potential of the plate.A second insulated plate B is now brought up slowly into a position parallel to A.

When B is very close to A but not touching it, it will be noticed that the leaf divergence decreases very slightly.We conclude from this that the potential of A has been decreased by the presence of B, and hence its capacitance has increased slightly.

Equivalence Capacitance of a Combination of Capacitors

Determine equivalence capacitance of a combination of capacitors

Factors affecting the capacitance of a parallel-plate capacitor.

There are three factors which affect the capacitance of a parallel-plate capacitor, namely;

Area of plates

Distance apart of the plates.

Dielectric between the plates.

Relative permeability (dielectric constant) of a medium

Relative permeability is the ratio of the capacitance of a given capacitor with the medium as dielectric to the capacitance of the capacitor with a vacuum as the dielectric.

It has no units since it is a ration of similar quantities.Paraffin wax has a relative permeability of about 2 while that of mica is about 8.

Combination of capacitors

Capacitors can be combined in series or in parallel so as to prevent overheating by being continuously overcharged.

Capacitors in Series.