- Introduction
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- Calculation of capacitance
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- Parallel plate capacitor
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- Cylinderical capacitor
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- Spherical capacitor
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- Capacitors in series and parallel combinations
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- Energy stored in a capacitor
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- Effect of Dielectric

- A capacitor (formerly known as condenser) is a device that can store electronic charge and energy.

- All capacitors consists of a combination of two conductors separated by an insulator.

- The insulator is called dielectric which could be oil, air or paper and many more such materials are there wich can act as a dielectric medium between conducting plates of a capacitor.

- Figure 1 below shows the symbol used to represent a capacitor.

- Now plates of the capacitor are connected to the terminals of a battery, shown below in figure 2, in order to charge it's conducting plates.

- As soon as capacitor is connected to the battery , charge is transferred from one conductor to another.

- Plate connected to positive terminal of the battery becomes positively charged with charge +Q in it and plate connected to negative terminal of the battery becomes negatively charged with cahrge -Q on it i.e. both plates have equal amount of opposite charge .

- Once the capacitor is fully charged potential difference between the conductors due to their equal and opposite charges becomes equal to the potential difference between the battery terminals.

- For a given capacitor Q∝V and the ratio Q/V is constant for a capacitor.

Thus,

Q=CV (1)

where the proportionality constant C is called the capacitance of the capacitor.

- Capacitance of any capacitor depends on shape , size and geometrical arrangement of the conductors.

- When Q is in coulumbs (C) and V is in volts(V) then the S.I. unit of capacitance is in farads(F) where

1F=1 coulumb/volt

- One farad is the capacitance of very large capacitor and it's submultiples such as microfarad(1μF=10
^{-6}) or picofarad(1pF=10^{-12}) are generally used for practical applications.

- For calculating capacitance of a capacitor first we need to find the potential difference between it's two conducting plates having charge +Q and -Q.

- For simple arrangements of conductors like two equivalent parallel plates kept at distance d apart or two concentric conducting spheres etc., potential difference can be found first by calculating electric field from gauss's law or by Coulumb's law.

- After calculating electric field , potential difference can be found by integrating ellectric field using the relation

V_{a}-V_{b}=∫E.dr

where the limits of integration goes from a to b.

- Once we know the potential difference between two conductors of the capacitor , it's capacitance can be calculated from the relation

C=Q/V (2)

- Calculation of capacitance of some simple arrangements would be illustrated in following few articles.

Class 12 Maths Class 12 Physics