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Frequency of permanent magnet

  1. Jun 15, 2013 #1
    Hello all,

    I am a newbie here but have a question that I was hoping someone could answer. Would a permanent magnet give off a single frequency or would it give off a spectrum of frequencies, like an incadescent light bulb can give off a spectrum of frequencies? I can measure the intensity of a permanent magnet using a standard magnetometer, like on my Iphone and get a an intensity of, lets say 1000 uT, but I am curious as to what frequency this corresponds to in terms of Hz. Or is the magnetic field given off by the magnet not even a part of the EM spectrum?

    Thanks for any insight into this question,

    Tord
     
  2. jcsd
  3. Jun 15, 2013 #2
    It corresponds to no frequency. A Tesla is a measure of magnetic field strength. Frequencies are a measure of something regularly changing in time.

    Like you guess, the magnetic field given off by a permanent magnet is not part of the EM spectrum. Its not an electromagnetic wave.
     
  4. Jun 15, 2013 #3
    Thanks for the information. So if it is not a part of the EM spectrum, what is being measured when you measure the intensity? Is there a magneton, something like the equivalent of a photon?
     
  5. Jun 15, 2013 #4
    Also, with respect to your comment of how frequencies are a measure of something regularly changing in time, when you turn on a light bulb, what is the time that is measured? Is it the time that the photons take to oscillate through space as it propagates from the source?
     
  6. Jun 15, 2013 #5
    Also, when they say that the earths magnetic field has a frequency of between 900 hz and 4.3 khz, what are the measuring?

    Sorry if these questions seem very basic, I am a scientist (PhD in biochemistry and molecular biology), but I am not familiar with physics other than what I learned in university a while ago.

    Thanks for all of your help,

    Tord
     
  7. Jun 15, 2013 #6

    SteamKing

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    Your question is not clear. When I turn on a light bulb, it comes on or it does not. What time should it measure? It is a light bulb, not a clock.

    Are you sure you understand the concept of 'frequency'? Frequency measures how often something repeats in a given amount of time. For example, the frequency of the rotation of the Earth is once per day.
     
  8. Jun 15, 2013 #7
    There are two frequencies I can think of that are associated with a light bulb. One is the frequency of the electricity that is powering it. The A/C current has a frequency because it changes regularly in time. The other is the frequency of the electromagnetic waves it emits (forget photons, we dont need a quantum description for this). Different light bulbs put out em waves of different frequencies. The frequency of the electricity powering the light bulb is not explicitly connected to the frequency of the emitted em waves.

    I guess that they are measuring the change in the magnetic field strength.
     
  9. Jun 15, 2013 #8
    So that I am clear, the magnetic field of a permanent magnet are not caused by an energy wave, because it does not have a frequency. So what is causing the magnetic field? If it isn't a particle and isn't an energy wave, what is the force that is causing the attraction or repulsion between two permanent magnets?
     
  10. Jun 15, 2013 #9

    mfb

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    A static magnet does not have a frequency in the same way an object lying on the floor does not have a frequency (it does not oscillate).

    To have a frequency, you need some oscillation of the field - you can rotate the magnet, for example. The frequency will be the rotation frequency then.

    Who says that?
     
  11. Jun 15, 2013 #10
    A magnetic field is "caused" by a magnetic moment. This is similar to the way that the electric field is "caused" by a charge or the gravitational field is "caused" by mass/energy.

    Be careful with the meanings of the words "energy" and "force", these have very specific meanings in physics. When you say this "If it isn't a particle and isn't an energy wave, what is the force that is causing the attraction or repulsion between two permanent magnets?", the question at the end of your sentence stands on its own. It is not entailed by the "if" clause at the beginning of your sentence. The force is the Lorentz force. Thats the name of it. The physics behind the attraction and repulsion of magnets is complicated. It generally has to do with the alignment of small dipoles in the material.
     
  12. Jun 15, 2013 #11
    http://en.wikipedia.org/wiki/Proton_magnetometer

    I guess I confused NMR with the frequency of a magnetic field. Thanks for helping clear that up for me. I'm still not clear on what is actually causing the magnetic attraction between two magnets. From what I have read (and I am probably wrong), it looks like magnetic fields can interact with the nuclei of atoms like protons and cause radio waves (basis of MRI), and they can also interact with matter like magnetite in permanent magnets (two physical magnets attract or repel), and they can also obvious interact with electrons (generation of electricity), but I can't seem to find a good explanation as to what the force is that is mediating these effects. Can anyone help explain this to me?

    Thanks!
     
  13. Jun 15, 2013 #12
    This might help a bit.
    http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magforcon.html#c1
    Click around and find topics on magnetism.

    Know that there are two different kinds of magnetic moments. One is from charges in motion. This is what is usually taught first in physics. A single electron sets up an electric field. Put that electron in motion and you have a magnetic field as well. Get a slew of electrons going in a circle and you have a current loop and you have a magnetic moment. This phenomenon takes place in an electromagnet (often with the help of a little magnetic material).

    The other kind of magnetic moment is intrinsic to particles. Its a basic property, meaning that no "cause" or "reason" is attributed to it (rather than speculation and hypothesizing of course). Some particles have a magnetic moment. This is called spin. In an NMR and in magnetic materials this type of magnetic moment is generally at play. An NMR lines up the magnetic moments of the particles in atomic nuclei. Then it measures how long it takes for them to drift back.
     
  14. Jun 15, 2013 #13

    Drakkith

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    Your question of what causes the attraction and repulsion between magnets is easily answered. It is the magnetic component of the electromagnetic force. The force coming from a permanent magnet is caused by the magnetic moments of the atoms adding up to be felt on a macroscopic scale.
     
  15. Jun 15, 2013 #14
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