Let there be a point charge of Q coulombs placed at the centre of an imaginary sphere of radius r metes. The electric intensity at any point on the surface is given by

E =    Q      
     4πε_oε_r r²

The direction of this electric field intensity is normal to the surface of the sphere at that point.

Though the number of lines of force crossing the sphere at that point are infinite but practically the tubes of force crossing per unit cross-section area is ε_oε_r times the field intensity at that point or tubes of force per unit area.

=ε_oε_r E= ε_oε_r       Q          =  Q 
                       4π ε_oε_r r²     4πr²

Surface area of sphere = 4πr²
Therefore, total number of tubes of force emanated from charge Q

=  Q   X 4πr² = Q
   4πr²

Hence the flux emanating from any charge is equal to its strength in coulombs.

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