A hollow cylinder has a charge q coulomb within it. If ϕ is the electric flux in unit of volt-meter associated with the curved surface B, the flux linked with the plane surface A in unit of volt-metre will be

Gauss's law states that the net electric flux through any closed surface is equal to the net charge inside the surface divided by ε0· i.e.,   ϕtotal =qε0Let electric flux linked with surfaces A, B and C are ϕA, ϕB and  ϕC , respectively. That isϕtotal =ϕA+ϕB+ϕC  Since ϕC=ϕA ∴  2ϕA+ϕB=ϕtotal =qε0  or   ϕA=12qε0-ϕB  But   ϕB=ϕ                       (given)  Hence, ϕA=12qε0-ϕ