The electric field $E$ due to a point charge at any point is defined as $\underset{q\to 0}{lim} \frac{F}{q}$, where $q$ is the test charge and $F$ is the force acting on it. What is the physical significance of $\underset{q\to 0}{lim}$ in this field expression? Draw the electric lines of a point charge $Q$ when (i) $Q>0$ and (ii) $Q<0$.