Physics 4, Section 2                                                        Jan 23, 2002

Electric flux Φ is the number of electric field lines cutting through a surface.

If the surface is closed, Gauss's Law gives a special case for the flux Φ_E through the surface due to the net charge q inside the surface:

        where

The point of Gauss's Law is that it uses the symmetry of special cases to simplify the calculation of electric field properties for those cases:

· Point charge :

· Line charge :

· Sheet of charge:

where λ and σ are linear and surface charge densities, respectively.

---

For a hollow conductor or a conductor with a cavity, the charge must be on the outside of the conductor. There is no charge on the inner wall of the cavity. This is easily shown using Gauss's Law.

Last modified on January 31, 2002