# Dielectric Constant-

Before you go through this article, make sure that you have gone through the previous article on Coulomb’s Law.

We have learnt-

• Dielectric constant refers to the relative electrical permittivity of the medium.
• It expresses the extent to which a material can hold electric flux in it.
• The dielectric constant of a material medium is defined as the ratio of absolute electrical permittivity of the medium to the absolute electrical permittivity of the free space.
• It is denoted by K or εr.  As it is the ratio of two like entities, it is a unit less and dimensionless quantity. It is a pure number.

The following table lists the value of dielectric constant for different materials-

#### Value of Dielectric Constant

Air / Vacuum 1
Metals Infinite
Water 80

Dielectric Constant in Terms of Force Between Two Charges

# Dielectric Constant In Terms of Force Between Two Charges-

Consider two charges q1 and q2 separated by a distance r from each other are placed as shown- #### Case-01: In Vacuum-

By Coulomb’s law, the force between these two point charges if placed in vacuum is given by- (Equation-01)

#### Case-02: In Any Other Medium-

By Coulomb’s law, the force between these two point charges if placed in any other medium is given by- (Equation-02)

Here, ε = absolute electrical permittivity of the medium

Dividing Equation-01 by Equation-02, we get- The ratio ε / ε0 is called relative electrical permittivityr) or dielectric constant (K) of the medium in which the charges are present. Thus, we have- So, one can define dielectric constant in terms of force between charges as follows-

#### Dielectric Constant

The dielectric constant of a medium is defined as the ratio of the electrostatic force between two point charges placed some distance apart in free space to the electrostatic force between the same two charges separated by the same distance in that medium.

#### Important Note-

From the above discussion, we conclude that-

When a material medium of dielectric constant K is placed between the charges, the force between them becomes 1/K times the original force in vacuum i.e. 