Continuous Charge Distribution: Any charge which covers a space with dimensions much less than its distance away from an observation point can be considered a point charge.

A system of closely spaced charges is said to form a continuous charge distribution. It is useful to consider the density of a charge distribution as we do for density of solid, liquid, gas, etc.

(i) Line or Linear Charge Density ( λ): If the charge is distributed over a straight line or over the circumference of a circle or over the edge of a cuboid, etc, then the distribution is called “linear charge distribution”. Linear charge density is the charge per unit length. Its SI unit is C / m.

(ii) Surface Charge Density ( σ) : σ= qSσ= dqdSorIf the charge is distributed over a surface area, then the distribution is called ‘surface charge distribution’.Surface charge density is the charge per unit area. Its SI unit is C / m2.

Total charge on surface S, q = ∫σdSS

(iii) Volume Charge Density ( ρ):ρ= qזρ= dqd זorIf the charge is distributed over a volume, then the distribution is called ‘volume charge distribution’. Volume charge density is the charge per unit volume. Its SI unit is C / m3