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Author Topic: Electric and Magnetic fields  (Read 5635 times)

Offline harryneild

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Electric and Magnetic fields
« on: 05/05/2006 16:35:18 »
Here are a few questions that i have wondered about.

How are magnetic poles, North and South, related to the electric charges, positive and negative? How does an electric field and a magnetic field differ from each other? How are they both combined to create an electromagnetic wave/particle?

I would appreciate any replies.

"Knowledge has to be improved, challenged, and increased constantly, or it vanishes." Peter F. Drucker
« Last Edit: 05/04/2007 21:56:46 by harryneild »


 

another_someone

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Re: Electric and Magnetic fields
« Reply #1 on: 05/05/2006 19:10:27 »
quote:
Originally posted by harryneild
How are magnetic poles, North and South, related to the electric charges, positive and negative? How does an electric field and a magnetic field differ from each other? How are they both combined to create an electromagnetic wave/particle?



The issues pertaining to wave particle duality are generally enough to blow my mind apart, so I will not try and explain how something (whether is be a photon, or an electron) can be at once a wave and a particle.  The closest I can get to understanding that contradiction is to look at how a soliton is created, but that may or may not have any bearing on how quantum waves become particles, and visa versa.

The relationship between electric fields and magnetic fields was first described mathematically by James Clerk Maxwell in the 19th century, although others like ěrsted and Faraday made significant qualitative contributions to the understanding of the observable effects.

Essentially, any electric current will create a magnetic field perpendicular to the direction of the flow of current.  Any magnetic field will induce an electric current when the strength of the field changes.

Einstein actually also produces a relativistic model of magnetism, and showed that magnetism was caused because the electric charge was moving at relativistic speeds, and so appeared to be closer than a stationary charge would be, and this created the appearance of magnetism.

What in fact is happening is that a current is formed by the movement of electrons, each of which contain an electric charge, and the magnetic field is generated by a moving electric charge, just as an electric field is created by a moving magnetic pole (the magnetic pole being an analogy to an electric charge).

What happens in an electromagnetic wave is that you have a constantly changing electric field (that changes in a sinusoidal fashion) that induces magnetic field that also changes in a sinusoidal fashion, but 90 degrees out of phase with the electric field, and perpendicular to it.  This changing magnetic field then induces an electric field that is also sinusoidal in nature, but again 90 degrees out of phase, and perpendicular to the changing magnetic field.  Thus each field (the electric and the magnetic) reinforces the other.





George
 

Offline Atomic-S

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Re: Electric and Magnetic fields
« Reply #2 on: 08/05/2006 06:29:59 »
In a traveling plane electromagnetic wave, the electric and magnetic fields are not 90 degrees out of phase with each other; they are in phase, but are pointed at right angles with respect to each other and also with respect to the direction of propagation. However this configuration is unstable and at once attempts to collapse. But pursuant to the laws of induction, as soon as the electric field begins to collapse, it begins to generate a magnetic field around it, much as a current would; the value of which is zero at the location of maximum original electric intensity, and stronglyh positive and negative to each side of it -- THIS is what is 90 degrees out of phase. Similarly, the collapsing original magnetic field induces a new electric field around it, likewise 90 degrees out of phase with the original. the result is that as the original wave configuration collapses, a new one arises 1/4 of a cycle later in time, and also 1/4 of a cycle further along in space.
 

Offline rosy

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Re: Electric and Magnetic fields
« Reply #3 on: 08/05/2006 16:18:35 »
I thought the E and M waves had to be 90* out of phase as well as at 90* spacially?? Otherwise you don't get the continuous transfer of energy from one to the other that you need for propagation?
 

another_someone

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Re: Electric and Magnetic fields
« Reply #4 on: 08/05/2006 16:57:14 »
I have yet to work out whether Atomic-S is saying they are or are not 90 degrees out of phase.

He says they are not, but then saying that this configuration is unstable, and then goes on to demonstrate that the stable configuration is ╝ wave (i.e. 90 degrees) out of phase.

I am probably missing some key point in Atomic-S's post, but I have not quite worked it out where it is



George
 

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Re: Electric and Magnetic fields
« Reply #4 on: 08/05/2006 16:57:14 »

 

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