Three equipotential surfaces are shown in (Fig. 3.28) A. Draw the corresponding field lines and estimate the field strength at a point A where the distance between the surfaces is 4 cm.
a.

Explanation

The field lines are perpendicular to the equipotential surfaces as shown in (Fig. 3.28)(b). In the vicinity of a, the surfaces are nearly flat, and so, in order to estimate the field strength, it is a reasonable approximation to use
`V_1 - V_b ~~ E. d`
or `E ~~ (V_a - V_b)/d = (8 V - 6 V)/(4 xx 10^-2m) = 50 Vm^-1`.