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# Physics/Electric fields and gauss's law

Question
I am having difficulty with these questions. Any help would be greatly appreciated.

1)   What is the net charge shown in this figure?

2)   What is the electric flux through each of the surfaces in the figure? Give each answer as a multiple of q/(epsilon_0)

1) Since the number of flux lines LEAVING the surface is 8 and the number of flux lines ENTERING the surface is 8 the net flux through the surface is 0. Therefore, the net charge contained within the surface must be 0.
2) The net charge contained in figure a is Qnet=+3q-2q=q, the net flux through the surface must be:
Fluxnet=q/eo
For figure b the net charge contained is Qnet=+q-2q=-q and so the net flux is:
Fluxnet=-q/eo
For figure the net charge contained is Qnet=0 and so the net flux will also be zero. The charges outside the closed surface do not matter at all since any flux line generated by charges located outside the figure both enters and exits the surface.

Physics