A hollow metal sphere is charged with $0.4 \mu C$ of charge and has a radius of $0.1 m$. Find the potential at the surface.

Two-point charges, one of +100 µC and another of -400 µC, are kept 30 cm apart. Find the points of zero potential on the line joining the two charges (assume the potential at infinity to be zero).

[3 Marks]

A charge $q=+1 \mu C$ is held at $O$ between the points $A$ and $B$ such that $AO=2 \mathrm{m}$ and $BO=1 \mathrm{m}$, as shown in Fig. (a). Calculate the potential difference  $\left(V_A-V_B\right)$. What will be the value of the potential difference $\left(V_A-V_B\right)$ if the position of $B$ is changed, as shown in Fig (b)

Two small spheres of radius $\text{'}a\text{'}$ each carrying charges $+q$ and $-q$ are placed at points $A$ and $B, d$ distance apart. Calculate the potential difference between points $A$ and $B$.

The sides of rectangle $ABCD$ are $15 \mathrm{cm}$ and $5 \mathrm{cm}$, as shown in Fig. Point charges of $-5 \mu C$ and $+2 \mu C$ are placed at the vertices $B$ and $D$ respectively. Calculate electric potentials at the vertices $A$ and $C$. Also calculate the work done in carrying a charge of $3 \mu C$ from $A$ to $C$.