What is capacitor?

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Capacitor stores electric charge. It is looks like battery it stores energy in a different way. It is stores much energy in battery. It releases charge very faster. Capacitor is very useful that’s why it is used in all circuit boards.

How does capacitor works

A water is flowing through a pipe water will flow until we shut down the valve. Then water can store in tank. However water can fill the tank and tank stores some water and continuously flowing water out in the pipe. If we close the valve water will stop pouring into the tank. It will steady supply water out until tank gets empty. Once the tank is filled again open and close the valve many times as long as completely empty the tank. We get interrupted supply water from the tank. We can use water tank to store water for interruption of water supply.

In circuits capacitor acts a water tank and it stores energy. It releases and more interruption of supply. A capacitor is like a storage tank it can used for smooth out interruption to the supply.

Let us see the simple ON/OFF circuit.

The light will ON/OFF very faster without a when there is no capacitor when the supply is power is turned OFF the light will immediately OFF. When the capacitor is fixed in a circuit, at that time power gets interrupted at that time circuit will remains without interruption because the capacitor will discharge the energy and empowering the circuit for at least short duration.



In basic capacitor it has two metal plates which are typically made from aluminium. It will be separated by dielectric insulated material such as ceramic. The dielectric means the material will polarize when in contact with an electric field.


One side of the capacitor is connected to the positive side of the circuit and other side is connected with negative side of the capacitor. The stripe in symbol indicates which side is negative. If we connect capacitor to battery the voltage will push the electron from negative terminal over the capacitor. The electron will build up in the one plate of capacitor and other plate will turn and release some electrons. Electrons can pass through capacitor through capacitor because of insulating material eventually the capacitor is the same voltage as the battery. Then no more electrons will flow.

There is a build up an electrons on one side this means we have stored energy. This can be released to do work because more electrons in one side to compare to other electron are negatively charged. This means we have one side negative and other side positive. So there is difference in potential or voltage difference between the two. The voltages we are compare difference between two points. If we measure 1.5 V batteries then we read the difference between the 1.5V each end. But if we measure same end there voltage is zero there is no difference.

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If we measure the voltage difference between the two it build-up of electrons we still get a reading even when we disconnect the battery.

We remember a magnets opposite poles they attract each other when they are same poles they will oppose each other. Same build of negative charged electrons. They are attracted to positive charged particles of atom of the opposite plate. They never reach each other because of the insulating material. This pole between the two sides electric field which holds electrons in place which other part is made.

If we place a small lamp in the circuit a power is exists electron will flow and reach the opposite side, so electrons flow through the electric lamp powering it and electrons will reach the opposite side of the capacitor. Once we connect the battery again capacitor begin to charge this allows the interpret power supply and capacitor will provide power during this interruption.

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Where do we use capacitor?

They look little bit different but easy to spot in circuit boards. It represented in diagram.

They also represented in engineering drawings also.

The large capacitor is used in induction motors, fans and conditioner units. Even large one used in power factor for larger buildings.

On the side of the capacitor we can find two values that are capacitance and voltage.

We can measure the capacitance of the capacitor in the unit of farads. This is mentioned as ‘F’ in capacitor. In circuit boards typically use micro-farads. It is used like letter ‘μ’ other value is voltage which we can measure in volts ‘V’. In the capacitor the voltage is the maximum value which capacitor can handle. The capacitor is rated at certain voltage it exceeds the capacitor will explode.


  • One of the common application is large buildings is for power factor correction.
  • If too many induction blowers are used the current and voltage waveform are fall synchronous each other, current will lag behind the voltage by using the capacitor bank to bring back into line.
  • Another very common application is converting AC to DC power.







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