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.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
Electric flux is a measure of the electric field passing through a given surface. It is calculated by multiplying the electric field strength by the surface area of the surface perpendicular to the electric field.
Electric flux is directly proportional to the amount of electric charge enclosed within a closed surface. This means that as the amount of electric charge increases, so does the electric flux passing through the surface.
The SI unit of electric flux is the volt-meter (V·m), which is also equivalent to the unit newton-meter squared per coulomb (N·m^2/C).
Gauss's law states that the electric flux passing through a closed surface is equal to the enclosed electric charge divided by the permittivity of free space. This law is useful in calculating the electric field strength and charge distribution in a given region.
The electric flux passing through a surface is dependent on the orientation of the surface with respect to the electric field. If the surface is perpendicular to the electric field, the full amount of flux will pass through it. However, if the surface is at an angle to the electric field, the flux passing through it will be reduced proportionally to the cosine of the angle.