Chapter-1|Electric Charges and Fields | NCERT 12th Physics:
Electric Field Due to a Point Charge:
Let a point charge q is placed at the origin O. We wish to determine it’s electric field at a point P, such that op=r.
Now if we placed a test charge q₀ at point P, then according to coulomb’s law the force on q₀ is
If E is the electric field at a point P due to charge +q at origin, then
From the above formula it is clear that the electric field at any point in space due to a charge depends only on the distance.