Question

In finding the electric field using Gauss law the formula $\left|\overrightarrow{E}\right|= \frac{q_{enc}}{\epsilon_{0}\left|A\right|}$ is applicable. In the formula $\epsilon_{0}$ is permittivity of free space, $A$ is the area of Gaussian surface and $q_{enc}$ is charge enclosed by the Gaussian surface. This equation can be used in which of the following situation ?

• A. For any choice of Gaussian surface.
• B. Only when the Gaussian surface is an equipotential surface.
• C. Only when the Gaussian surface is an equipotential surface and $\left|\overrightarrow{E}\right|$ is constant on the surface.
• D. Only when $\left|\overrightarrow{E}\right| =$ constant on the surface.

Answer 1

Answer: (C)

Only when the Gaussian surface is an equipotential surface and $\left|\overrightarrow{E}\right|$ is constant on the surface.

Answer 2

$\left|\overrightarrow{E}\right|$ should be constant on the surface and the surface should be equipotential.