# Surface Charge Density Formula

## Surface Charge Density Formula

According to electromagnetism, charge density is defined as a measure of electric charge per unit volume of the space in one, two or three dimensions. To be specific, the linear surface or volume charge density is the amount of electric charge per surface area or volume, respectively.

Surface charge describes the electric potential difference between the inner and outer surface of different states like solid and liquid, liquid and gas or gas and liquid. The surface charge density is present only in conducting surfaces and describes the whole amount of charge q per unit area A.

Hence, the Surface charge density formula is given by,

σ = q / A.

Where,

q = charge and

A = surface area.

Electric field regarding surface charge density formula is given by,

σ = -2 ϵ0 E.

Where,

ϵo = permittivity of free space,

E = electric field.

Example1

Calculate the surface charge density of a conductor whose charge is 5 C in an area of 10 m2.

Solution:

Given:

Charge q = 5 C,

Area A = 10 m2

Surface charge density formula is given by,

σ = q / A

= 5 / 10

Therefore, σ = 0.5 C/m2

Example 2

Calculate the surface charge density of sphere whose charge is 12 C and radius is 9 cm.

Solution:

Given:

Charge q = 12 C,

The surface charge density formula is given by,

σ = q / A

For a sphere, area A = 4 π r2

A = 4 π (0.09m)2

A = 0.1017 m2

Surface charge density, σ = q / A

σ = 12 / 0.1017

= 117.994

Therefore, σ = 117.994

#### Practise This Question

If lens I with focal length + 15 cm and lens II has focal length + 30 cm. find out which lens has more power?