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Offline DoctorBeaver

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Questions about magnetic fields
« on: 12/08/2007 07:20:02 »
These questions were prompted by UKMickey's thread about the density of magnetic material.

1) Does the temperature of the material affect its magnetic strength?
2) Does a magnetic field have a frequency?
3) What effect, if any, does light have on a magnetic field?

P.S. Please note that at least I managed to post this in the appropriate forum!
« Last Edit: 12/08/2007 07:34:35 by DoctorBeaver »


 

Offline Soul Surfer

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Questions about magnetic fields
« Reply #1 on: 12/08/2007 09:21:31 »
The temperature has a big effect on ferromagnetic (and I presume ferrimagnetic)materials.  This is because to generate these properties  the basic paramagnetic properties of the individual atoms have to link together to produce a bulk effect and the gradual increase in molecular vibrations with temperature evenually disrupts the long range order.  This takes place at a particular temperature knwon as the curie temperature for a particular ferromagnetic material.  Ferrimagnetic materials are materials that also develop long range order due to magnetism but this order is like two bar magnets clamped together and cancels out magnetism at long range.  In feromagnetism the order is such that all the magnets are aligned in very similar directions and add up to make a powerful magnet.

The magnetic effect does not have a specific frequency associated with it but ferromagnetic materials do have a response time and take a finite (and in molecular terms quite slow )respose time to changes of external driving field.  As all materials are dynamic there are frequecies associated with molecular agitation (thermal noise) and electron spin and level changes but they are not really what I think you mean by a frequency.  ie is a magnetic field intermittent on a very fine time scale?

A magnetic field can affect light but light other than the excessive energy input to a frromagnetic material causing it to get hot and become demagnetised does not affect a magnetic field.
 

Offline DoctorBeaver

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Questions about magnetic fields
« Reply #2 on: 12/08/2007 09:28:02 »
Thanks, Ian. I understood most of that (what's the difference between ferromagnetic & ferrimagnetic?).

By frequency I meant the same as you get different frequencies of light.
 

Offline Soul Surfer

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Questions about magnetic fields
« Reply #3 on: 12/08/2007 09:59:50 »
I thought that I had explained that.  Ferrimagnetic materials are materials in which below a certain temperature there is structural organisation in the orientations of the atoms but this does not produce a large magnetic field extrending a long way from the object because the orientation is such as to cancel out the magnetic fields of the individual atoms in groups.   

If I have two bar magnets of the same size and power and they are separated from each other each has quite a powerful magnetic field and will affect a compass needle at a distance of several times their length.  If you now put them together such that they attract each other you will be putting the south pole with the north pole.  You will then find that the magnetic field of the combined magnet is much less at a distance than the two magnets separately because the combined fields of the two magnets are cancelling each other.  If you go very close to the two magnets the field is still very strong.
 

Offline lightarrow

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Questions about magnetic fields
« Reply #4 on: 12/08/2007 11:01:50 »

3) What effect, if any, does light have on a magnetic field?
P.S. Please note that at least I managed to post this in the appropriate forum!
I don't think you are so layman, I notice you improve your scientific knowledge every day. Will you be so kind to answer our boring questions when you will be much more expert than any of us?  :)

About light and mag field, if you remember, light is an electromagnetic field, which varies in time and in space: the fields on average go up and down along a space ≈ 5000 atoms long; so, considering regions of space as small as those values (or more(*)), light do change magnetic and electric fields strongly.

Edit.
(*) I intended: "or more small", that is, "or smaller".
« Last Edit: 13/08/2007 11:21:25 by lightarrow »
 

Offline DoctorBeaver

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Questions about magnetic fields
« Reply #5 on: 12/08/2007 12:01:49 »
Sorry, Ian, it was your use of words like "order" that I didn't quite understand.


3) What effect, if any, does light have on a magnetic field?
P.S. Please note that at least I managed to post this in the appropriate forum!
I don't think you are so layman, I notice you improve your scientific knowledge every day. Will you be so kind to answer our boring questions when you will be much more expert than any of us?  :)


I doubt that will ever happen where physics is concerned as I'm a real dumbo when it comes to the maths. However, I know a bit about psychology.

As for improving my scientific knowledge every day, I think everybody should try to learn something new every day. I just happen to take a special interest in science, especially particle physics, quantum stuff & cosmology.
« Last Edit: 12/08/2007 12:05:01 by DoctorBeaver »
 

Offline Soul Surfer

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Questions about magnetic fields
« Reply #6 on: 13/08/2007 09:27:51 »
By "long range order" I meant when atoms arrange themselves in particular patterns and orientations in large groups.  Another common example would be a crystal
 

Offline DoctorBeaver

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Questions about magnetic fields
« Reply #7 on: 13/08/2007 09:45:39 »
Ah. Thanks.
 

lyner

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Questions about magnetic fields
« Reply #8 on: 19/08/2007 00:28:29 »
Quote
3) What effect, if any, does light have on a magnetic field?
In a 'linear medium' such as space, light ( a high frequency, short wavelength electromagnetic wave) and the field round a 'permanent' magnet (a very low frequency and long wavelength electromagnetic wave - I say low frequency because it was not always there and there must have been a change in field at some time) would not interact - the principle of superposition applies.  The  field vectors just add up in a linear fashion. This is what happens when two light beams or radio waves cross each other's paths without any interaction. Your view across the room is not affected by what other people can see - if the air is clear- that is.
In a non -linear medium,   however, and when the fields are high, you can get interaction between the two waves / fields. This has been found when very high power radio transmissions pass through the same region of the Ionosphere where there are ionised particles in the Earth's magnetic field. Cross modulation and intermodulation occurs -producing interference onto the weaker signal and interference signals at other frequencies.
 

Offline DoctorBeaver

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Questions about magnetic fields
« Reply #9 on: 19/08/2007 11:10:57 »
Can you give an example of a non-linear medium?
 

lyner

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Questions about magnetic fields
« Reply #10 on: 21/08/2007 17:36:30 »
As I said - the ionosphere is a non-linear medium. The 'displacement' is not proportional to the 'impressed force, or field, in this case'. It's the way the electrons behave in the plasma up there. There aren't enough of them to obey the normals laws that apply in metals etc. so it goes non-linear.
There are plenty of non linearities in everyday life - the junction in a diode is non linear;  it doesn't follow OHM's law, that's a localised non-linearity. The non-linearity is more 'distributed in a ferrite, or even a piece of iron is non linear once it starts to saturate.
When you run out of easily movable magnetic dipoles in a material, the  magnetic flux  is no longer proportional to the magnetic field.
Multiple fields won't add up to the sum of their individual components. They all produce 'spurious products' under the right conditions. A strong magnetic field will easily change the level of a weaker radio signal.  .
« Last Edit: 21/08/2007 17:38:25 by sophiecentaur »
 

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Questions about magnetic fields
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