Question
Tue April 08, 2014 By: Renuka Ganesh

While Calculating electric flux through a given surface, should we use the formula for calculation of flux depending on the gaussian surface considered(e.g. CUBE i.e FLUX=ELECTRIC INTENSITY AT THAT POINT*AREA OF CUBE)  or should we use the formula, FLUX=CHARGE/permittivity of medium?

Expert Reply
Tue April 08, 2014
Both of them are the same .
First one is flux through an area element whereas second is the total flux,for a closed surface.
The electric flux through an area element ΔS is given by
Δφ =E. ΔS
So this formula will give the flux through an area element
On the other hand to find the total flux through the sphere,we have to add up flux through all the different area elements.
Thus the formula φ, Flux = Charge/permittivity of medium, gives the total electric flux through a closed surface.
This law is called Gauss's law, φ =q / εo
This is true for any closed surface.
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