Important points about electric field :
1. Note that the electric field E due to q, though defined operationally in terms of some test charge qo, is independent of qo. This is because F is proportional to qo, so the ratio F/qo does not depend on qo.
The force F on the charge qo due to the charge q depends on the particular location of charge qo which may take any value in the space around the charge q.
Thus, the electric field E due to q is also dependent on the space coordinate r.
For different positions of the charge qo all over the space, we get different values of electric field E. The field exists at every point in three-dimensional space.
2. For a positive charge, the electric field will be directed radially outwards from the charge. On the other hand, if the source charge is negative, the electric field vector, at each point, points radially inwards.
3. Since the magnitude of the force F on charge qo due to charge q depends only on the distance r of the charge qo from charge q, the magnitude of the electric field E will also depend only on the distance r.
Thus at equal distances from the charge q, the magnitude of its electric field E is same. The magnitude of electric field E due to a point charge is thus same on a sphere with the point charge at its centre; in other words, it has a spherical symmetry.
Electric field due to system of charges : If there are a number of stationary charges, the net electric field (intensity) at a point is the vector sum of the individual electric fields due to each charge.
Vector E = Vector [E1+E2+E3+.....+En]
or Vector E = 1/4πεo [ q1/r1^2 (r1 cap) +q2/r2^2 (r2 cap) + q3/r3^2 (r3 cap) +.....qn/r n^2 (r n cap)]
