POLARIZATION or DIELECTRIC POLARIZATION

Consider a dielectric placed in an  external electric field E0 (say between the plates of a charged capacitor). Due to external field, there will be shifting of the centres of gravity of positive and negative charges. The positive charges are displaced  in the direction of the applied field whereas the negative charges will get displaced in a direction opposite to the applied field E0 ( try to make the figure). Therefore, the positive charge is induced on one surface while negative charge on other.

This phenomenon of appearance of the charge on the surfaces of dielectric induced by the external electric field is called polarization  or dielectric polarization.

The charge  on the plates of the capacitor is called free charge and charge induced on the surfaces of the dielectric is called bound charge.

We can also say that when the  atoms are placed in an electric  field, they acquire an induced electric dipole moment in the direction of the field.  This process is called the dielectric polarization and atoms are said to be polarized. Continue reading “POLARIZATION or DIELECTRIC POLARIZATION”

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Static dielectric constant

Static dielectric constant

Definition: The ratio of the capacitance of a given capacitor (with the material filling the entire space between its plates) to the capacitance of the same capacitor in vacuum is called static dielectric constant or relative permittivity of the material.

A dielectric is characterized by its dielectric constant which is also called relative permittivity.

Derivation: Continue reading “Static dielectric constant”

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Electric field between two oppositely charged parallel plates

Electric field between two oppositely charged parallel plates:

In the last article, I have explained and derived the expression for the capacitance of parallel plate capacitor with dielectric and without dielectric. Today we will discuss and derive the relation for electric field between two oppositely charged parallel plates.

Let +q and –q be the charges on the plates of a parallel plate air capacitor. Let A be the area of the plate.

The magnitude of the electric field, E, between the parallel plates

is given by

E1 = q/ ε0A

If  σ is the charge per unit area, then q = Aσ and thus

E1 = σ/ ε0

This is the expression for the electric field between two oppositely charged parallel plates.

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Capacitance of a Parallel Plate Capacitor

Parallel plate capacitor consists of two conducting plates parallel to each other and separated by a distance which is small compared  with  the dimensions of the plate.

Let A be the area of each plate separated by a distance d in vacuum and +q and -q are the charges given to the plates.

The charges on each plate are attracted by the charges on the other plate. So the charges spread out uniformly on the inner surfaces of the plates and produce an electric field E between the two plates. Continue reading “Capacitance of a Parallel Plate Capacitor”

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