Question

Define electric flux. Write its S.I. units. A spherical rubber balloon carries a charge
that is uniformly distributed over its surface. As the balloon is blown up and
increases in size, how does the total electric flux coming out of the surface change?
Give reason.

Answer 1

Electric flux is the dot product of the electric field vector and the vector normal to the surface through which the field lines pass.  That gives the amount of electric field lines passing through a surface.

units are :      N-m^2 / Coul 

Let the charge distributed on the surface be = q
Let initial radius be = R0.
So initial surface charge density = σ= q/(4πR0²)

As the balloon is blown up, the radius increases.   The surface charge density reduces.  If we take a ficticious Gaussian surface (spherical closed) around the balloon with radius just a little more than R, then the total electric flux that comes out of the surface 
     =  integral  E. dS =  q/ε   

That depends only on the charge enclosed.    So that remains same.