1.9 Electric Field due to Different Systems

          Now let us find the electric field due to different charge distributions. We shall start from electric field due to a point charge and then electric field due to a number of point charges, electric field due to a dipole and interaction between dipole and uniform field. We further discuss electric field due to symmetric charge distributions like line charge, sheet of charge and charged conduction sphere.

1.9 (a) Electric Field at a point due to a Point Charge

                     Let 'P' be a point at a distance 'r' from a point charge 'q' in air. To find the electric field at 'P', imagine a unit positive charge kept at 'P'.

        Note:
   The electric field at a point P due to a point charge is independent of the charge kept at the point P.

1.9 (b)  Electric Field at apoint due to a System of Point Charges

                Consider a system of charges q1,12, q3,.......qn. Can you find net electric field intensity at any point due to a system of charges?
                    Electric field is a vector quantity. Hence electric field at any point due to a system of charges can be found using super position principle.
                 
      Vectors Ep= E1p + E2p + E3p + ............ Enp

Electric field at a point due to a number of charges is the vector sum of electric field due to individual charges.
Note:
  1. In order to find the electric field at a point, imagine a unit positive charge kept at that point. The force acting on it will give the electric field at that point both in magnitude and direction.
2.If we keep a charge 'q' in an external electric field "E' Then the force actingo on that charge F= qE

Vectorialy F=qE
3.With a point charge as center, all along the surface of a sphere the electric field has the same magnitude (value) but directions normal to the surface of the sphere.