Page 11 - Electrostatics 11 class

Grade 11 © GC Shiba

1 2
∴ =
4 ∈ 2

Permittivity: It is the ability to permit the electric force by medium or free

space.

Dielectric constant/ relative permittivity (k):

Dielectric constant of a medium is defined as the ratio of force acting between
any two charges in free space at a certain distance to the force acting between

two same charges in a medium at same distance.

1 2
4 ∈ 2
Mathematically, k (∈ ) = = 0

1 2

4 ∈ 2

∈
∴ =
∈ 0

Note: The dielectric constant depends on other factors like temperature,

frequency of voltage applied, moisture etc. It increases with increase in
temperature in solid and decreases with increase in temperature in gas and
liquid.

The value of dielectric constant for air is equal to 1. Its value is greater than 1 for
the other materials. E.g., for water k = 80. It means if the air is replaced by water,

then the force of attraction or repulsion between the two charges is reduced by 80

times as, =
80

1 Coulomb: Two similar charges are said to be 1 coulomb if they exert the force
9
of 9 × 10 N on each other at a distance of 1 meter in free space.

Limitations of Coulomb's law:

☻ It holds good for stationary point charges only.
☻ it is not universal as it depends on properties of intervening medium.

11 Electrostatics