A charge of +5μC is located somewhere inside a closed hollow cube with sides 30 cm long. What is the electric flux through the closed surface of this box?
5.6×10**5 x Nm**2/C

Can somebody tell me, why?

Question

A charge of +5μC is located somewhere inside a closed hollow cube with sides 30 cm long. What is the electric flux through the closed surface of this box? 
5.6×10**5 x Nm**2/C

Can somebody tell me, why?

anonymous · Answer

The flux through a closed surface can be found with Gauss's Law. It is proportional to the enclosed charge, regardless of the shape and size of the surface. The electric field is very larger nearer to a charge, but a surface father away has bigger area. As long as the same amount of charge is inside the surface, the flux is the same. 
The E field of a a charge points towards or away from that charge. If you have a surface near a charge that doesn't contain that charge, the amount of flux going into the surface will be the same as the amount of flux going out of the surface, so the net flux is zero.