Sunday 11 May 2014
How Does A Capacitor Work?
Do you often wonder “how does a capacitor work”? In this article we will find answer to this interesting question.
One may already found the answer in many books. It states something like “a capacitor works by storing energy electro-statically in an electric field”. I don’t know about you, but that sentence didn't make me any wiser when I was starting out with electronics.
I like to answer the question of “how does a capacitor work?” by saying that a capacitor works like a tiny rechargeable battery with very very very low capacity.
The time it takes to discharge a capacitor is usually only a split second. And so is the time to recharge it.
What Is A Capacitor?
Just like the Resistor, the Capacitor, sometimes referred to as a Condenser, is a simple passive device that is used to “store electricity”. The capacitor is a component which has the ability or “capacity” to store energy in the form of an electrical charge producing a potential difference (Static Voltage) across its plates, much like a small rechargeable battery.
There are many different kinds of capacitors available from very small capacitor beads used in resonance circuits to large power factor correction capacitors, but they all do the same thing, they store charge.
A capacitor is made up of two metallic plates. With a dielectric material in between the plates.
When you apply a voltage over the two plates, an electric field is created. Positive charge will collect on one plate and negative charge on the other.
And this is what the physicists mean when they say that “a capacitor works by storing energy electrostatically in an electric field”.
Capacitor Construction:
The parallel plate capacitor is the simplest form of capacitor. It can be constructed using two metal or metallised foil plates at a distance parallel to each other, with its capacitance value in Farads, being fixed by the surface area of the conductive plates and the distance of separation between them. Altering any two of these values alters the the value of its capacitance and this forms the basis of operation of the variable capacitors.
Also, because capacitors store the energy of the electrons in the form of an electrical charge on the plates the larger the plates and/or smaller their separation the greater will be the charge that the capacitor holds for any given voltage across its plates. In other words, larger plates, smaller distance, more capacitance.
The Capacitance of a Capacitor
Capacitance is the electrical property of a capacitor and is the measure of a capacitors ability to store an electrical charge onto its two plates with the unit of capacitance being the Farad (abbreviated to F) named after the British physicist Michael Faraday.
Capacitance is defined as being that a capacitor has the capacitance of One Farad when a charge of One Coulomb is stored on the plates by a voltage of One volt. Capacitance, C is always positive and has no negative units. However, the Farad is a very large unit of measurement to use on its own so sub-multiples of the Farad are generally used such as micro-farads, nano-farads and pico-farads.
What Does A Capacitor Do?
As we already discussed capacitor is stored to store charge, For example:
if you have a circuit with a microcontroller running some kind of program. If the voltage for the microcontroller drops for only a split second, the microcontroller restarts. And you don’t want this.
By using a capacitor, the capacitor can supply power for the microcontroller in the split second that the voltage drops so that the microcontroller doesn’t restart. This way it will filter out the “noise” on the power line.
Apart from storing charge a capacitor can also be used for filtering.
Capacitors and resistors is combined to form filters that target specific frequencies. For example in an audio system you can target the high frequencies to remove them.This is called a low-pass filter.
