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Non-conservative fields,

  1. May 17, 2012 #1

    FOIWATER

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    has anyone ever seen an example like this worked out



    it's pretty amazing, I was just wondering everyone else's thoughts.. I would intuitively agree w/ the engineers who said he could not be right!

    How could the voltmeter read two separate potentials from the same two points.

    Just wanted to hear everyone else's intuitive reaction.

    EDIT: http://ocw.mit.edu/courses/physics/...etism-spring-2002/lecture-notes/lecsup315.pdf
     
    Last edited by a moderator: Sep 25, 2014
  2. jcsd
  3. May 17, 2012 #2
    That guy is a cool teacher. He goes out of his way to make principles clear and real, and he has a real understanding of what he's teaching. I wish I had one like him for EM.

    I like his point how the professors were stumped when they saw this, because it shows how even the best experts can have misconceptions when it comes to physics.

    edit: can, not cab. Also, He did convert 10 cm^2 incorrectly, but that was just a minor detail.
     
    Last edited: May 17, 2012
  4. May 17, 2012 #3

    FOIWATER

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    I agree..
     
  5. May 18, 2012 #4
    I gone through this in the Classical Physics forum section here the Christmas before, go dig it up. I gave up, it is not that easy. I even did the experiment myself. I am not convinced he is right, but I ran out of theory and he is a MIT professor.

    Bottom line in terms of EE, I found the scope probe lead form part of the loop and cannot be taken out. I suggest to go to the Classical Physics section and do a search for Levine. You'll find me there arguing in over 40 posts!!!! I posted diagram of my experiment and finding. I spent the whole Christmas on that one.
     
  6. May 18, 2012 #5

    FOIWATER

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    Yeah I cannot understand it either yungman, I don't understand how he has the voltmeters set up. I'll look for your post Thanks
     
  7. May 18, 2012 #6

    jim hardy

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    i too am skeptical and was then, too.

    A changing flux induces voltage in his test leads. That's what he has demonstrated.

    His meter reports the voltage that arrives at the instrument, not what's at the far end of its leads.
    You can demonstrate that with a toroid power transformer and any dmm just pass pne lead through the donut and short them. That makes one turn around the core.
    I wont accuse him of sophistry, but either he or me is confused. And his math is better than mine.

    If he explained why he excludes induced voltage from Kirchoff's law it'd help me.
     
  8. May 18, 2012 #7
    This is the thread I spent so much time in it:

    https://www.physicsforums.com/showthread.php?t=453575&highlight=Walter+Lewin

    I don't have enough physics background to keep on and I gave up. But I am not convinced. I think he is full of it. If you have the time to sort through the posts, you'll see the experiment I did and my observation in detail. Problem is the scope probe's ground lead, I demo the voltage change as I move the ground leak over from one side to the other and I explained why the ground lead is part of the problem. You'll see my drawing starting around page 8!!!! Yes it gone on and on and on and on!!!
    I spent the whole Christmas on that just the first round, and picked up months later!!! Just too bad I don't have the high level of theoretical physics background to keep on. And being an engineer, I can't spend that kind of time argue about things that is almost semantics.
     
    Last edited: May 18, 2012
  9. May 19, 2012 #8

    FOIWATER

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    I see what you were saying in the other thread - He removed the voltage source, IE the battery, but did not replace it with anything... if you have a voltage induced, you have to represent this as a coil, like in a transformer schematic? I mean, you can place the coil anywhere you like - but you have to put it somewhere. And - it has to represent the one volt induced? I don't know this is bothering me
     
  10. May 19, 2012 #9
    To argue with them, you have to be very careful, those physics people don't do equivalent circuit. It makes sense, EE books take short cuts but putting equivalent circuits like voltage soruce, current sources, batteries etc. that is really not real to make it easier. You have to talk in terms of Maxwell's equations etc.

    I finally repeated the experiment and documentation in #post 224!!! If you ever get to page 14!!!:rofl:

    https://www.physicsforums.com/showthread.php?t=453575&highlight=Walter+Lewin&page=14

    I gave my observation in the attached file to show all the "illusion" were because of the ground lead of the probe that I had not been able to take it out of the circuit and that's the very thing that cause the false reading in his demo.

    Have fun reading and follow the thread. Don't you have have better things to do? They wore me out.:rofl:
     
    Last edited: May 19, 2012
  11. May 19, 2012 #10
    BTW, I never challenge his claim, I challenge his experiment, to me, his experiment don't mean a thing as you cannot get the measuring equipment out of the picture, you are reading the error caused by the setup. If ever there is a way ( I even attempt in the follow up posts by differential amp and fancy grounding) to avoid magnetic induction of the probe lead, I claim the outcome would be different.

    If you go to post #246, I tried to use differential amp.

    https://www.physicsforums.com/showthread.php?t=453575&highlight=Walter+Lewin&page=16

    I couldn't believe I must have wrote over 100 posts on that thread!!!
     
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