Characteristics of electric field is as following :

$(i)$ The charge $Q$, which is producing the electric field is called a source charge and the charge $q$, which tests the effect of a source charge is called a test charge.

However, if a charge $q$ is brought at any point around $Q$ itself is bound to experience an electrical force due to $q$ and will tend to move. A way out of this difficulty is to make $q$

negligibly small. The force $\vec{F}$ is then negligibly small but the ratio $\frac{F}{q}$ is finite and defines the

electric field : $\overrightarrow{\mathrm{E}}=\lim _{q \rightarrow 0} \frac{\overrightarrow{\mathrm{F}}}{q}$

$(ii)$ Note that the electric field $\overrightarrow{\mathrm{E}}$ due to $\mathrm{Q}$ though defined operationally in terms of some test charge $q$ is independent of $q$. This is because $\vec{F}$ is proportional to $q$, so the ratio $\mathrm{F} / q$ does not depend on $q$.

The field exists at every point in three-dimensional space.

$(iii)$ For a positive charge, the electric field will be directed radially outwards from the charge as shown in figure$ (a)$.

For a negative charge, electric field vector at each point, points radially inwards as shown in figure $(b)$.

$(iv)$ Since the magnitude of the force $\mathrm{F}$ on charge $q$ due to charge $\mathrm{Q}$ depends only on the distance $r$ of the charge $q$ from charge $Q$ the magnitude of the electric field $\vec{E}$ will also depend only on the distance $r$.

$\therefore \mathrm{E} \propto \frac{1}{r^{2}}$