State the meaning of electric potential at a point.
Two parallel metal plates A and B are separated by a distance $d$ in a vacuum, as shown in Fig. 6.1. Plate A is earthed and plate B is at a potential of $+V_0$. Point P is in the central region between the plates at a distance $x$ from plate B. The potential at point P is $V$. On Fig. 6.2, show how the potential $V$ varies with $x$ for values of $x$ from $0$ to $x = d$.
Two isolated solid metal spheres M and N, each of radius $R$, are placed in a vacuum. Their centres are separated by a distance $D$, as shown in Fig. 6.3. Each sphere carries charge $+Q$. Point P lies on the line joining the centres of the two spheres, and is at a distance $y$ from the centre of sphere M. On Fig. 6.4, show how the electric potential at point P varies with distance $y$ for values of $y$ from $y = 0$ to $y = D$.