A uniformly charged solid sphere of radius $R$ has potential $V_0$ (measured with respect to $\infty$) on its surface. For this sphere the equipotential surfaces with potentials $\frac{{3{V_0}}}{2},\;\frac{{5{V_0}}}{4},\;\frac{{3{V_0}}}{4}$ and $\frac{{{V_0}}}{4}$ have rasius $R_1,R_2,R_3$ and $R_4$ respectively. Then

An infinite non-conducting sheet has a surface charge density $\sigma  = 0.10\, \mu C/m^2$ on one side. How far apart are equipotential surfaces whose potentials differ by $50\, V$

Given below are two statements: one is labelled a

Assertion $(A)$ and the other is labelled as Reason$(R)$

$Assertion$ $(A)$ : Work done by electric field on moving a positive charge on an equipotential surface is always zero.

$Reason$ $(R)$ : Electric lines of forces are always perpendicular to equipotential surfaces.

In the light of the above statements, choose the most appropriate answer from the options given below 

Describe schematically the equipotential surfaces corresponding to

$(a)$ a constant electric field in the $z-$direction,

$(b)$ a field that uniformly increases in magnitude but remains in a constant (say, $z$) direction,

$(c)$ a single positive charge at the origin, and

$(d)$ a uniform grid consisting of long equally spaced parallel charged wires in a plane

Figure shows a set of equipotential surfaces. The magnitude and direction of electric field that exists in the region is ………