Question

what is the important of gaussian surface

Answer 1

Gaussian surface is closed surface in three dimensional space through which the fluex of a vector field is calculated

Answer 2

Answer:

The expression for electric field intensity can be obtained by applying Coulomb's law only in simple cases. In the situations, where Coulomb's law or principle of superposition cannot be applied to calculate the electric field, the same is achieved by using Gauss' law. For this, one has to evaluate the surface integral.  

So that surface integral can be evaluated easily, a closed surface is chosen cleverly around the charge distribution. The surface so chosen is called the Gaussian surface.