Conceptual question about electric flux

AI Thread Summary
Electric flux through a disk differs from that through a cube or sphere due to the nature of the surfaces involved. The disk is an open surface, allowing for a net flux, while the cube and sphere are closed surfaces that enclose a volume. Since there are no charges inside the cube or sphere, the electric field lines entering one face must exit another, resulting in zero net flux. This distinction highlights the importance of surface type in calculating electric flux. Understanding these concepts is crucial for studying electric fields and their interactions with different geometries.
faller217
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I am studying electric flux through both a disk, cube, and sphere. I understand how the flux is calculated in a disk, but I don't understand how the flux through a cube with the point charge outside the cube is equal to zero when the disk is not. Is this because the disk is 2-D?

Thank you for your help
 
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faller217 said:
I am studying electric flux through both a disk, cube, and sphere. I understand how the flux is calculated in a disk, but I don't understand how the flux through a cube with the point charge outside the cube is equal to zero when the disk is not. Is this because the disk is 2-D?

Thank you for your help
You've got the right idea. The disc is an open surface whereas the cube and sphere are closed surfaces, this means that they enclose a volume. Now since there are no charges inside these surfaces, any electric field lines that pass through one of the faces of the cube, must also pass out of another face. The same is true of the sphere. Therefore, there is as much flux entering the cube and sphere as there is leaving it, hence the net flux through those surfaces is zero.

Do you follow?
 
I follow perfectly. Thanks very much for explaining! :)
 

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