Q: In finding the electric field using Gauss law the formula $|\vec{E}| = \frac{q_{enc}}{\epsilon_0 |A|}$ is applicable . In the formula ∈_{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 $\vec{E}$ is constant on the surface

(d) Only when $\vec{E}$ = constant on the surface

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Ans: (c)

Sol: The magnitude of electric field should be constant and surface should be equipotential surface .