Derive an expression for electric field intensity at a point due to point charge.

Explanation

Electric field intensity at a point due to a charge is the force acting on a unit positive test charge when placed at the point.
Let us determine force on a charge `q_(0)` placed at P at a distance r from .q.. It is given by :
`vecF=(Kq q_(0))/(r^(2))hatr`
Electric intensity, `vecE=(vecF)/(q_(0))`

or `vecE=(K q q_(0))/(r^(2)q_(0))hatr`
or `vecE=(Kq)/(r^(2))hatr`
or `vecE=(1)/(4piepsi_(0))xx(q)/(r^(2))hatr" "[becauseK=(1)/(4piepsi_(0))]`.