Consider a small length δl of a conductor of radius a meters and having a charge of q coulombs per meter of its length.

Total charge over the length δl of the conductor = qδl

According to Gauss’s theorem
The total flux crossing the surface = charge enclosed by the surface

or     Ψ = qδl

Surface area crossed by the flux = 2παδl

Flus density, D = Total flux crossing the surface     =  qδl    =   q
                        Surface area crossed by the flux    2παδl   2πα

Field intensity at distance of meters from the conductor is given by

E =  D   =     q       
    ∈_o∈_r    2πα∈_o∈_r
   

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