Page 8 - Electrostatics 11

Grade 11 © GC Shiba

1 2
∴ =
4 ∈ 2
0
For medium in SI unit, k is replaced by new constant 1 Where ∈ is
4 ∈
permittivity of the medium.

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.

Mathematically, k (∈ ) =

1 2
4 ∈ 2
= 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.

1 Coulomb: Two similar charges are said to be 1 coulomb if they exert the
9
force 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.

8 Electrostatics