For a collection of N point charges Q₁ ,Q₂ ,.........Q_N located at ,,......, the electric field intensity at point is obtained as

........................................(2.6)

The expression (2.6) can be modified suitably to compute the electric filed due to a continuous distribution of charges.

In figure 2.2 we consider a continuous volume distribution of charge r(t) in the region denoted as the source region.

For an elementary charge , i.e. considering this charge as point charge, we can write the field expression as:

.............(2.7)