For a collection of n point charges, the electric dipole moment is defined as follows, \(\vec{p}=\stackrel{i=n} \sum _{i=1}q_i\vec{r}_i\) where,  \(\vec{r}_i\) is the position vector of charge q_i from the origin.

(i) No two electric field lines intersect each other. lf two lines cross at a point, then there will be two different electric field vectors at the same point.
(ii) As a consequence, if some charge is placed in the intersection point, then it has to move in two different directions at the same time, which is physically impossible. Hence electric field lines do not intersect.

Electric field at the point P at a distance r from the point charge q is the force experienced by a unit positive placed at that point P and is given by
\(\vec { E } =\frac { \vec { F } }{ q_{ 0 } } =\frac { kq }{ { r }^{ 2 } } \hat { r } =\frac { 1 }{ 4\pi { \varepsilon }_{ 0 } } \frac { q }{ { r }^{ 2 } } \hat { r } \)
where \(\hat{r}\) is the unit vector pointing from q to the point of interest P.

  Coulomb force Gravitational force (i)  It is attractive or repulsive. It is always attractive . (ii) It depends on the nature of the medium in
which the two charges are kept at rest. It is independent of the medium. (iii)  It obeys Newton's third law. It does not obey Newton's Third Iaw. (iv) Coulomb force is given by,
\(\overrightarrow{F_{12}}=\frac{1}{4 \pi \varepsilon_{0}} \frac{q_{1} q_{2}}{r^{2}} \hat{r}_{21}\) Gravitational force is given by,
\(\vec{F}=G \frac{m_{1} m_{2}}{r^{2}}\hat{r}\)

The charge of an electron is the elementary charge in nature. Therefore, charge on any body is the integral multiple of an electron. The charge on any body can be expressed by the formula,
q = ne; where, n is the number of electrons, e is the charge on one electron.
n = 0, ±1, ±2, ±3, ±4, ...
This is called quantization of charge.