Question

Define electric flux through a surface. Give the significance of a Gaussian surface. A charge outside a Gaussian surface does not contribute to total electric flux through the surface. Why?

Hint:

The electric flux through a surface is proportional to the charge enclosed by that surface, as per Gauss’s law.

Answer 1

Electric flux \( \Phi_E \) through a surface is defined as the product of the electric field \( E \) and the area \( A \) of the surface, and the cosine of the angle \( \theta \) between the electric field and the normal to the surface: \[ \Phi_E = E \cdot A \cdot \cos(\theta) \] A Gaussian surface is an imaginary closed surface used in Gauss's law to calculate electric flux. The significance of a Gaussian surface is that it helps in calculating the electric flux and, using Gauss’s law, can be used to determine the electric field due to symmetrical charge distributions. A charge outside a Gaussian surface does not contribute to the total electric flux because the electric field lines from the external charge do not pass through the surface, and thus, the net flux through the surface remains zero.