flux doubt

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in d ques

"charge q is located at distance l/2 from the center of square above its center. Determine electric flux through the square ."

i know d formal way i.e
(cmplete the square into a cube and proceed)

but whats wrong i n this thinking

flux= field lines in- field lines out

hence 'zero'?

pls helpp....

#Physics #Electricity and magnetism

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2 Answers

106

Asish Mahapatra ·2011-02-27 08:30:32

well what is flux ? flux = âˆ«E.da

so if you take a single surface. then the flux through it is equal to the integral of the perpendicular component of the electric field over the surface area.

What you are trying to do is applying Gauss Law. which states that flux through a CLOSED surface = lines out - lines in

for a plane surface, it can be considered to be two surfaces separated by a thickness tending to zero. Hence the lines in = lines out hence zero.

But this is a closed surface, so it actually means that the flux through the upper surface = flux through lower surface (the two surfaces are actually the same). Thats why you are geting the ambiguity. but simply apply the defiinition of flux.. :)