Question

An equipotential surface is represented by an equation $x^2+y^2+z^2=4$. The source charge for it must be

• A. a line charge
• B. a point charge
• C. an infinite sheet
• D. either line charge or point charge

Answer 1

The correct option is B a point charge

Potential at a distance $r$ from a point charge $q$ is

$V=\frac{kq}{r}$

For the equipotential surface $V$ should be constant throughout the surface and for this given case, it is satisfied for spherical surface where $r=$ constant at surface of sphere.


The equation of equipotential surface $x^2+y^2+z^2=4$ represents a sphere with $r=2$. So, it will only be possible when source is point charge.

$\therefore$ $\left(b\right)$ is the correct option.

Why this question? Tip : Equipotential surface due to line charge is a cylindrical surface and due to infinite sheet it is plane surface.