Electrostatics - Electric Flux Density D

Discussion in 'Physics' started by Nirvana, Aug 21, 2006.

  1. Nirvana

    Thread Starter Well-Known Member

    Jan 18, 2005
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    0
    Previously in the thread titled Electrostatics - Coulomb's Law, Coulomb's Law was defined aswell as the Electric Field Strength.
    If we take the Vector quantity E which is the electric field strength (a vector as it has both magnitude and direction) and multiply it by the permittivity ε, we get a new vector D.
    So D = εE = ε * Q/4π ε r2 , the ε cancles out leaving us with D = Q/4π r2

    Notice how the electric flux density is independant of the permittivity ε. What does this mean?
    Well say we had an electric field acting on a type of material, then from the formula for the electric field strength we know that the value of E is dependant upon the material used by the value of the permittivity ε. But the electric flux density D will remain the same no matter what material you use.
    Basically although changing the types of materials will effect the electric field strength E, it will not affect the electric flux density D.
     
  2. Hansu

    New Member

    Sep 21, 2008
    1
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    what do you think about E on boundary?
    The book said the tangential component of an E field is continuous across an interface even though the permittivities are in different to each medium.
    E1(tan) = E2(tan)
    I'm confused of it.
     
  3. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    The flux density D tells you how many lines of force (field lines, if you think like that) pass through an area. Thus, whatever the material is, if the area is the same and flux is the same then D is the same for all these materials. However, E is different for each material because each material permits in a different degree (ε) the flux to pass through it.
     
  4. triggernum5

    Active Member

    May 4, 2008
    216
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    Think about it like this.. If you have a strand of any dielectric 1m long, and you attach 0V to one end, and 50kV to the other, regardless of the permittivity there will be a voltage drop of 50kV/m..
     
  5. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
    1
    Just a general note about what I have learned from studying electromagnetics. Electromagnetic laws are extremely simple to remember, but the mathematics behind their use is very intense. You must know your vector calculus very well to implement them!

    Simplifications, such as when one does basic magnetic modeling, should not be confused with what was mentioned above. This can usually be done with ease.

    Steve
     
  6. REUBEN

    New Member

    Dec 22, 2008
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    looking for ssomething related to the derivation of the calculus of GAUSS's THEOREM
     
  7. steveb

    Senior Member

    Jul 3, 2008
    2,433
    468
    It means you have stumbled across a law of nature. :)

    This is a simplified form of one of Maxwell's equations; specifically Gauss' Law. The total charge enclosed in a volume equals D (normal to the surface of the volume) integrated over the surface.
     
  8. Skeebopstop

    Active Member

    Jan 9, 2009
    358
    3
    I like mik3's answer :) I think in picatures.
     
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