i. The net flux crossing an enclosed surface is equal to \(\frac{q}{\epsilon_0}\) where q is the net charge inside the closed surface.
ii. Consider a charge +q at the centre of concentric circles as shown in figure below.
As the charge inside the sphere is unchanged, the flux passing through a sphere of any radius is the same.
iii. Thus, if the radius of the sphere is increased by a factor of 2, the flux passing through is surface remains unchanged.
iv. As shown in figure same number of lines of force cross both the surfaces.
Hence, total flux is independent of shape of the closed surface radius of the sphere and size of closed surface.
