Electric Field for a point charge
If I have just one point charge setting up the field, and a second point charge comes into the field, I know (from Coulomb’s Law) that
Fon 2 = k q1 q2 / r122 and
Fon 2 = q2 * Eat 2 which gives:
E at 2 due to 1 = k q1 / r122 for a point charge.