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Relationship electricity and magnetism

  1. Oct 24, 2013 #1
    Hello, I have started reading a beginners book (from the "stop faking it" series) on electricity and magnetism. Its supplied with funny little experiments to help me understand the topic. But I have trouble understanding the intimate relationship between electricity and magnetism. I believe I understand the model of atoms, protons and electrons and how electrons behave.

    I'll try to show part of the picture I have gained now: a negatively charged object (let's say a rubbed balloon) can induce a charge in another object because the electrons repel the electrons in another object and attract the protons. As a result, the distance between the electrons of the balloon and the protons of the other object is smaller and they attract each other. So I get the topics of charges, electrons' tendency to move and make objects neutral, and electric fields as a result of charging an object.

    Now when it comes to magnetism I see how bar magnets interact in the sense that the magnetic force tends to "line them up". Also I took the point that electrons themselves are like tiny magnets. When a coil is connected to a battery and wrapped around, for example a screw, it creates a bigger magnetic field and leaves the screw magnetized for a while.

    Now what I do not understand is when you have a coil of wire and you move a magnet in and out, a current starts to flow. Is the magnet inducing magnetism in the coil of wire? So the electrons "want to" line up with the magnetic field of the magnet, and thats why they start flowing and create current?

    I also do not understand this sentence in the book I am reading: "A changing magnetic field generates an electric field". I see a magnetic field a result of a charged object (like the balloon has a magnetic field around it).

    Some help on clearing this up would be great!
     
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  3. Oct 24, 2013 #2

    tiny-tim

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    w

    hi t1mm3h! :smile:
     
  4. Oct 24, 2013 #3

    tiny-tim

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    hi t1mm3h! welcome to pf! :smile:
    no: a stationary charged object generates an electric field, a moving charged object generates a magnetic field

    the magnetic field of a permanent magnet is generated by the electrons moving in tiny loops around their atoms

    the magnetic field of an electromagnet is generated by the electrons in the solenoid moving in large loops

    so long as the magnet is not moving, or the current in the electromagnet is not changing, there is no electric field (ie only a magnetic field)

    when it changes, an additional electric field is created
    no, the magnet is inducing an electric field

    that electric field makes the electrons move in the usual electric way :wink:
     
  5. Oct 24, 2013 #4
    Thanks for your reply tiny-tim.

    1) So if the magnet induces an electric field, is the solenoid (the stationary object) becoming charged temporarily (as the magnet moves in)?

    2) To go to a lower level: as far as I can see, a magnet can cause electrons to "line up" with the magnetic field. Is this why an electric field is induced?
     
  6. Oct 24, 2013 #5

    tiny-tim

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    hi t1mm3h! :smile:
    no, the wire in the solenoid remains electrically neutral

    all that happens is that the positive charges remain stationary, while the negative charges (the electrons) start moving along the wire

    no charge is created
    no, the electrons "line up" whether the magnet is moving or not

    (and it is only their spins that line up)

    anyway, the electric field is created (by a moving magnet) whether there are any electrons there or not
     
  7. Oct 24, 2013 #6
    Okay so what causes the electrons to move? Is it the induced electric field? I guess I still don't fully understand how an electric field (yes I read the pf definition) comes into existence due to a magnet. Does the movement of the magnet solely create a electric field? If I hold a bar magnet in my hand and move it up and down, do I create an electric field...?
     
  8. Oct 24, 2013 #7

    tiny-tim

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    yes, the electrons move only because there is an electric field
    yes you do

    basically induction happens because it happens, there isn't really a "why" (other than the mathematical structure of space-time)
     
  9. Oct 24, 2013 #8
    I know physics isn't here to answer why questions, it just explains what we observe for a great deal.

    So we can conclude that a changing magnetic field generates an electric field because we see charges in the wire moving. And we know that charges move because of electric fields. Right?

    Thanks for the great help so far! I think I can continue reading my book now and start learning more. Any recommendations on material for understanding electricity/magnetism?
     
  10. Oct 24, 2013 #9

    tiny-tim

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    yes … that's science! :smile:
    what stage of education are you at?
     
  11. Oct 24, 2013 #10
    Great I get it. Thanks again tiny tim.

    Well I already studied at university level but I studied social sciences. I dropped physics and chemistry about 10 years ago in the beginning of secondary school. Now I want to (re)learn at least the basics of science (physics, chemistry and biology) by doing self-study.
     
    Last edited: Oct 24, 2013
  12. Oct 24, 2013 #11

    tiny-tim

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    (i wouldn't bother about magnetism)

    you could try scientific american (monthly) …

    it has quite long but well-explained articles, and you could use them as a basis for further study

    (and if you want to subscribe, pf members can get 20% off)
     
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