Dielectric substance and dielectric constant

* “Dielectric substance”:
Those substance that doesn't not conduct electricity but on placing them in a strong electric field they showing electric effect are known as Dielectric substance.
Exa: water, mica, paper etc

These substances are of two types
1) Polar dielectric: In these substances the center of mass of positive charges (proton) and center of mass of negative changes(electron) are separated to each other. Thus their molecules behave like a dipole.
Exa: HF, HCL, etc.

2) Non-polar dielectrics : In these substance their molecules containing the centre of mass of proton and the centre of mass of electron coincide to each other. when these substance kept in an electric field then the centre of mass of proton produce some displacement towards the electric field but centre of mass of electron displaces opposite to the electric field and the substance get polarized.
Exa: H2, N2, O2 etc.

* “ Dielectric constant or Relative permittivity :
It is the tendency of penetrate the electric field through the medium. insulators having lower tendency to pass the electric field.                    it is denoted by K or £r.

 “Measurement ”: Dielectric constant of the medium is the ratio of electrostatic force acting between two point charges in air/ vacuum to the electrostatic force acting between those charges in the presence of medium .                  it is the Pure ratio thus  it has no unit.

Dielectric constant, K = F(air)/F(medium)

K = 1×q×q'/4π£o×r²÷ 1×q×q'/4π£×r²
K = 1/£o÷1/£
K = £/£o = £r
£ = £ok

*Note: Dielectric constant of metal, k = infinity,
for water, k = 80 ,
 for air, k = 1



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