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Electric flux density(D)

The force acting on a charge moving in an electromagnetic field, as given by the Lorentz force is associated two field vectors electric flux density(D) and the magnetic field intensity(H).


Electric flux density(D):



  • Electric flux is the normal (Perpendicular)  flux per unit area.

  • If a flux of \Phi passes through an area of A m^2 normal to the area then the flux density ( Denoted by D) is:D = \dfrac{\Phi}{A}

  • If a electric charge is place in the center of a sphere then the electric flux on the surface of the sphere is:


D = \dfrac{\Phi}{A} = \dfrac{Q}{4 \pi r^2} , where r =radius of the sphere.


The SI unit of electric flux is Coulomb per meter square.


Relation between Electric flux density and electric field intensity:


If we compare the formula for the


Electric flux Density given above with the formula for the Electric Field intensity ,  We see that:
D = \dfrac{Q}{4 \pi r^2}  and  E = \dfrac{Q}{4 \pi \epsilon_0 \epsilon_r r^2}


Where , \epsilon_0 = Permittivity of vacuum and  \epsilon_r = relative Permittivity.


Thus, We can conclude that:
D = \epsilon _0 . \epsilon _r . E      And,      E = \dfrac{D}{\epsilon_0 . \epsilon_r}

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