The electric field and electric potential at any point due to a point charge kept in air is $20 N{C}^{-1}$ and $10 J{C}^{-1}$ respectively. Compute the magnitude of this charge.

A point charge $Q$ is placed at point $O$ as shown in figure, Fig. $2.101.$ Is the potential difference $V_A-V_B$ positive, negative or zero if $Q$ is 

(i) positive?

A point charge $Q$ is placed at point $O$ as shown in figure, Fig. $2.101.$ Is the potential difference $V_A-V_B$ positive, negative or zero if $Q$ is 

(ii) negative ?

Two point charges $2 \mu c$ and $-2\mu c$ are placed at points $A$ and $B$, $6 cm$ apart.

(i) Draw equipotential surface of the system.