A positive charge Q is located at the origin....

[GaussianSurface]

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Hi, I've been doing this excersice but I'm not quite sure about my answer
It says: A positive charge Q is located at the origin of a three-dimensional coordinate system. Consider and imaginary square surface of side length L and parallel to the plane y-z, as is shown in the figure. Find the total electric flux passing through the Area A.

Well, as the formula of electric flux is Flux= E*A I think that given it's a infinite plane it should be E= σʹ/2€ and the area of a square A= L^2.
Then the result should be this Flux= σʹ/2€*L^2?

 

[J Hann]

Can you find the radius of a sphere with an inscribed cube with sides 2L?

 

[Gregoriorosso]

the radius of the sphere is √2 L
the surface of the sphere is 8*π*L^2

 

[J Hann]

You really don't need the sphere, but it may help to illustrate the symmetry involved.
You know the total flux from Gauss' Law.
Then, what fraction of that flux passes thru the specified surface.

 

[TSny]

Following @J Hann , imagine a square of side 2L as shown. The area A that you are interested in is shaded.

Construct a closed surface around the point charge that uses this large square as part of the total closed surface.