Capacitor
Capacitor can be defined as the device which is used to store electrical energy by electrostatic stress in the dielectric. It consists of two conducting surfaces separated from a layer of an insulating medium called dielectric. The conducting surfaces either be round or in rectangular plates or spherical or cylindrical shapes.
A parallel-plate capacitor is shown figure. One plate is fastened to the positive end of the supply and other is joined to the negative end or is earthed. Experimental results indicates that plate B which is earthed , plate A is capable of withholding more charge more than When B is not there. There is momentary flow of electrons from A to B, when a capacitor is put across a battery.
As negatively charged electrons are withdrawn from A, it acts as a positive and these electrons reaches at B, it behaves as negative. The transient flow of electrons provides rise to the charging current. The strength of charging current is maximum when the two plates are uncharged but it then decreases and finally ceases when p.d.(potential difference) across the plates becomes slowly equal and opposite to the battery e.m.f.(electro magnetic flux)
capacitance
The property of a capacitor to store electricity may be called its capacitance. The capacitance of capacitor may also defined as " the amount of charge required to create p.d. between its plates.
If we provide Q coulomb of charge to one of the two plate of capacitor and a potential difference of volt V is established the two, then its capacitance is
C = Q/V = charge/p.d.
so we can say capacitance is the charge required per unit potential difference. Its unit is farad which is equal to coulomb/volt. So 1 Farad = 1 coulomb/volt
Definition of Farad.
Farad is named in the honor of Michael Faraday. Which is defined as the capacitance of a capacitor which needs a charge of one coulomb to establish a p.d. of one volt between its plates.
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