Question

(a) Define electric flux. Is it a scalar or a vector quantity ? 

A point charge q is at a distance of d/2 directly above the centre of a square of side d, as shown in the figure.

Use Gauss' law to obtain the expression for the electric flux through the square.

(b) If the point charge is now moved to a distance 'd' from the centre of the square and the side of the square is doubled, explain how the electric flux will be affected.

Answer 1

(a) Electric flux: The electric flux linked with a surface is the number of electric lines of force passing through a surface normal and is measured as the surface integral of the electric field over that surface, i.e.

Electric flux ϕ is a scalar quantity. Now calculate the electric flux through the square of side d, we draw a cube of side d such that it completely enclosed the charge q. Now from Gauss's law

(b) If the charge is now moved to distance d from center of square and side of square is doubled, then electric flux is unchanged i.e. remains the same, because electric flux depends only on the amount of charge and but not on side of the square, OR position of charge.