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Faraday's law

  1. Dec 21, 2014 #1
    can someone tell me , why must the magnetic flux be taken into account instead of magnetic field ?? thanks...
     
  2. jcsd
  3. Dec 21, 2014 #2

    Dale

    Staff: Mentor

    This is up to the person doing the analysis. If you use the integral form consider the flux. If you use the differential form then you consider the field.
     
  4. Dec 21, 2014 #3
    I don't really understand. why must we be introduced the flux? if a loop is at 30degree of let say 1T of B , can't we simply take the 1T for calculation for the induced emf? and I have a new problem. if a solenoid is set up, and I move near a magnet to the side of it instead of entering its centre of circular . is there any emf induced? no? thank you for your reply.
     
  5. Dec 21, 2014 #4

    Dale

    Staff: Mentor

    This is a consequence of Stokes theorem. If you have a differential law that describes the curl of a vector field then Stokes theorem proves that there will also be an equivalent integral law that describes the flux. They are different but equivalent ways of looking at the same thing.

    http://mathinsight.org/stokes_theorem_idea
     
  6. Dec 23, 2014 #5
    thanks for your help. can you tell me how is the Lorentz law done experimentally during his time? or give me a link telling this? thanks.. I have been searching this. but still couldn't get any result. thanks .
     
  7. Dec 23, 2014 #6

    vanhees71

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  8. Dec 23, 2014 #7
    I was looking at a physics book and found that Maxwell's equations are based on Faraday's law but Faraday's experiment using a torrid, wires and battery is not emitting light yet Maxwell's electromagnetic theory of light is based on Faraday's law but again Faraday's experiment with the torrid is not emitting light. So, I found an article that stated Hertz's experiment proves light in an electromagnetic phenomenon but first, I could not find Hertz's paper 1887 anywhere on the internet which is extremely odd since this experiment is perhaps one of the most important papers, in physics, since Maxwell's equations are used everywhere, I think, right? But everywhere I looked and looked and looked: the only thing that I could find was that Hertz's experiment verified the fact that Maxwell's electromagnetic theory of light since radio waves propagate at the velocity of light (c) and produce wave effects similar to light. I did an Hertz's spark gap experiment, in an independent study physics class, and I did get a A+ on my paper but the problem is that my physics teacher (he has a phd from MIT but is some kind of hippie dropout, after he meet his hippie wife; they live in a wood house that looks like a flying saucer, and own goats that what my friends say) said that the squiggly line that produced the light of Hertz's spark gap are, in fact, electrons but Faraday's induction effect is not an ionization effect or does it really matter? I don't really know why it really matter but he got all exited and was spitting all over the place and just keep going on about ionization. What is ionization anywhere? Something about electrons but the spark gap is emitting electrons. I just don't get it but he owns goats. So how can a person who owns a bunch of silly goats know anything!
     
    Last edited: Dec 23, 2014
  9. Dec 24, 2014 #8
    The most important factor concerning the production of electricity is magnetic flux. Magnetic flux is what causes current flow. I should say that the change of magnetic flux is what causes current flow. The greater the magnetic flux and the faster the change of magnetic flux across a wire or a coil will determine the output. So a good understanding of magnetic flux will determine the success of your Alternator / generator. while magnetic field is actually generated by the current
     
  10. Dec 24, 2014 #9

    vanhees71

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    The paper by Hertz is easily found with the help of google scholar (it's anyway a great search engine for scientific papers and also patents, by the way; even when looking for HEP papers it's sometimes better than INSPIRE):

    H. Hertz, Ueber sehr schnelle electrische Schwingungen, Ann. Phys. (Leipzig) 267, 421 (1887)
    http://dx.doi.org/10.1002/andp.18872670707

    What has the expertise of your teacher to do with the pets he keeps? He is right in saying that the sparks you see are gas discharges.
     
  11. Dec 24, 2014 #10
    Can you tell me if Faraday's induction experiment is emitting light?
     
    Last edited: Dec 24, 2014
  12. Dec 24, 2014 #11

    Dale

    Staff: Mentor

    The EM waves produced by Faraday's experiment would be far below the visible range.
     
  13. Jan 8, 2015 #12
    Then is Maxwell's equations based on an induction analogy?
     
  14. Jan 8, 2015 #13

    Dale

    Staff: Mentor

    The physical phenomenon of induction is described by Maxwell's equations. It isn't what I would call an analogy.
     
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