Year+13+Capacitors

__**Capacitors**__



In a way, a capacitor is a little like a battery. Although they work in completely different ways, capacitors and batteries both store electrical energy. You know that a battery has two terminals. Inside the battery, chemical reactions produce electrons on one terminal and absorb electrons on the other terminal. A capacitor is much simpler than a battery, as it can't produce new electrons -- it only stores them.

Most circuits in all your electrics will contain a capacitor, they come in many types, shapes and sizes. A capacitor is an electric component which has the ability to store charge. They store charge by having plates, separated by a distance. The amount of charge they can store for a given voltage is a measure of their capacitance. Capacitance can be increased by making the area of the plates larger, the distance between them smaller and using a different dielectric between the plates.

The charging and discharging or capacitors are the basis for the concept behind touch screens. When your skin comes into contact with the screen, a circuit is formed (as your skin conducts electricity)

Even nature shows the capacitor at work in the form of lightning. One plate is the cloud, the other plate is the ground and the lightning is the charge releasing between these two "plates." Obviously, in a capacitor that large, you can hold a huge amount of charge!

Make Sure you visit this site, it is very informative! How Stuff Works - Capacitors media type="youtube" key="ciMxaPvEPUs?rel=0" height="349" width="425"

After reading the "how stuff works page", read and take notes on page 146 in Rutter. Familiarise yourself with the concept behind charging a capacitor.

When a battery is connected to a series resistor and capacitor, the initial current is high as the battery transports charge from one plate of the capacitor to the other. The charging current asymptotically approaches zero as the capacitor becomes charged up to the battery voltage. Charging the capacitor stores energy in the electric fieldbetween the capacitor plates. The rate of charging is typically described in terms of a time constant, RC. The time constant  (in  seconds  ) is given by resistance (in  ohms  ) multiplied by the circuit  capacitance  (in  farads  ), i.e. ** τ = //R × C//**. It is the time required to charge the capacitor , through the  resistor  , to 63.2 (≈ 63) percent of full charge; or to discharge it to 36.8 (≈ 37) percent of its initial voltage. (These values are derived from the mathematical constant // [|e] //, specifically 1 − //e// − 1 and //e// − 1 respectively).