The property of the capacitor is called as **capacitance**. The ability of a capacitor to store energy is measured by **capacitance**. It is defined as the ratio between the charge stored Q by a capacitor to the voltage V across the terminal. The **capacitance** is denoted as “C”.

**Capacitance** can be mathematically expressed by

Also, it is defined as the ratio of charge stored by capacitor to voltage V across the same capacitor.

Note: When the voltage across the capacitor or the capacitor voltage reaches or equal to source voltage means capacitor does not charge. No charge flows.

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.

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.

The unit of **capacitance** is Farad (F). To Honor Sir Michal Faraday (the inventor of most popular electrical law of electromagnetic induction), the unit of capacitor is named in Farad. Actually, one Farad is very large unit which means the size of the capacitor comes very bigger and most capacitors are rated in micro Farad (uF= 1 x 10^{-6}) or micro farad (pF) or Pico Farad (pF) 1 pF = 1 x 10-12F

If Q=1 coulomb and V=1 volt, then **capacitance** is 1F. That’s we can say that 1 Farad is equal to 1 Coulombs/1volt.

## One Farad

One Farad is defined as the **capacitance** of a capacitor between the plates of which there appears a potential difference of I volt when it is charged by 1 coulomb of electricity.

### Calculate capacitance value for two parallel plates capacitor

Let us consider a parallel plate capacitor in which the upper and lower plates are separated by some distance of d meters. There is a potential difference of V volts between the two plates, therefore work required in transferring coulomb of charge from one plate to another is V Joules; since the work is the product of force and distance d the force experienced by the charge is the electric field strength E is given by ..

The electric flux density D is given by

The relation between electric flux density and electric field in terminals is given by

The parallel plate capacitor

Here the relative permeability of the material vary according to the type of dielectric material is used to construct a capacitor.