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Electrostatic Potential And Capacitance

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Potential Energy of an Electric Dipole in an External Field:
Whenever an electric dipole is kept in a uniform external field E at an angle , it tries to align itself back parallel to the electric field. Why does it happen? What gives it energy to work against this external field to align itself. It is due to the Potential Energy stored in the dipole. Whenever an external agent applies torque on the dipole to make it inclined at an angle , the work done gets stored in the dipole as its Potential Energy. Let us see how we derive the expression for potential energy through this video.

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Potential Energy of an Electric Dipole in an External Field
2 mins
Electrostatic Shielding:

Conductors with cavities show a very interesting behaviour under an external electric field. They have a unique property that all charges reside only on the outer surface of the conductor with cavity.
This leads us to the result that the electric field inside the cavity is always zero, whatever be the size and shape of the cavity and whatever be the charge on the conductor and the external fields in which it might be placed.

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So here we can see that the external field due to charge +q has no effect on the cavity inside the conductor. However it induces some charge on the outer surface of the conductor. Let's have a quick look at this topic through a story.

Electrostatic Shielding
2 mins
Capacitance of a spherical capacitor:
We have can build a capacitor using any system of two conductors separated by an insulator. A spherical capacitor is one such configuration of two concentric spherical conductors. If we charge the inner spherical conductor with a charge +q, then it will induce a charge -q on the inner surface of the outer spherical conductor. The charge on the outermost surface is of no use while calculating the capacitance of the system. Only the electric field in the gap is considered. Let's understand the derivation of the capacitance of this system through this video.

Class 12 Physics | Capacitance | #8 Capacitance of a Spherical Capacitor | For JEE & NEET
4 mins