Electric Flux

 

fluxAni.gif (5428 bytes)

   

coneAni.gif (12876 bytes)It is often simpler to find the flux through one surface of an object than through another.  In the case of the cone the flux through the base  (Area = pi2.gif (831 bytes) R2) is the same as the flux through the lateral surface, but it is much easier to calculate the flux through the base.

phi.gif (841 bytes) = E Alateral cos theta2.gif (833 bytes)   = E (pi2.gif (831 bytes) R2)


Previously Asked Questions

Q:     If the electric field in a point P in space is zero, does this mean that there are no charges in the vicinity of point P?

A:    No, it may just be that the individual fields created by individual charges cancel each other at point P.

Q:     Why does excess charge on an isolated conductor reside on the conductor's surface?

A:    Any solid object is a crystal.  The total energy of a crystal can be calculated at any point of the solid.  This is done by using quantum mechanics, in the chapter of physics called "Solid State Physics."  The total energy in a point inside the crystal is the result of contributions of all atoms surrounding that point.  The total energy in a point at the surface of the crystal is only the result of contributions of atoms belonging to the crystal.  There are no such atoms outside the surface of the crystal.  Therefore, the total energy at the surface is less than the total energy inside the crystal.  Since in a conductor the electrons can move, they will move spontaneously toward a region of minimum energy which is the surface.

In an insulator the energy at the surface is also smaller than the energy inside the bulk.  However, the electrons in an insulator are not "free" to move toward the minimum energy surface region, and will remain strongly bonded to their parent atoms.

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References

Equations

Gauss' Law   epsilon2.gif (824 bytes) 0 phi.gif (841 bytes) = qenc
Electric flux through a Gaussian surface  phi.gif (841 bytes) = oint.gif (71 bytes) E cdot.gif (46 bytes) dA

Applications of Gauss's Law

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List of Topics

Measurements Electric Potential Magnetism Electrical Circuits (AC) Optical Instruments: Mirrors and Lenses
Electrostatics Capacitance Sources of Magnetic Fields Maxwell's Equations Interference
Electric Fields Current and Resistance Magnetism in Matter Electromagnetic Waves Diffraction
Electric Flux Electrical Circuits (DC) Electromagnetic Induction Interaction of Radiation with Matter: Reflection, Refraction, Polarization  

 

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