Three infinitely long wires with linear charge density $\lambda$ are placed along the $x$-axis,$y$-axis,and $z$-axis respectively. Which of the following denotes an equipotential surface?

Surfaces $A$ and $B$ are at the same potential $V'$. The work done in moving a charge $q$ from $A$ to $B$ is ........

Draw an equipotential surface for a uniform electric field.

What is an equipotential surface? Draw equipotential surfaces for:
$(1)$ $A$ single point charge
$(2)$ $A$ dipole (charges $+q$ and $-q$ at a small distance)
$(3)$ Two $+q$ charges at a small distance
$(4)$ $A$ uniform electric field.

Two point charges $-Q$ and $+Q / \sqrt{3}$ are placed in the $xy$-plane at the origin $(0,0)$ and a point $(2,0)$,respectively,as shown in the figure. This results in an equipotential circle of radius $R$ and potential $V = 0$ in the $xy$-plane with its center at $(b, 0)$. All lengths are measured in meters.
$(1)$ The value of $R$ is. . . . meter.
$(2)$ The value of $b$ is. . . . . .meter.

$A$ point charge $+q$ is placed at the origin. The work done in moving another point charge $-Q$ along the straight line path $AB$ from point $A$ with coordinates $(0, a)$ to point $B$ with coordinates $(a, 0)$ is .......