Electromagnetic radiation

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  • #1
Ezio3.1415
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1. In the theory of electromagnetism, we say light(and others with different λ) propagates through anything by the alternation of the electric and magnetic field... I am still reading things abt the theory,haven't finished yet... But some things seem not clear... It seems 'em' is saying the propagation of energy is not discrete(as I visualize it)... How do we fit photons here? I mean how do I explain the propagation of energy is discrete when I am explaining using electromagnetic wave...

2. A problem a friend gave me...
You are sending a light beam in the front direction, using a flash light. If the electric field of the light is in the up direction, what will be the direction of the magnetic field?
(A) Left (B) Right (C) Front (D) Up (E) Down
Obviously the answer's not front or down or up... left or right... give ur explanation...
 

Answers and Replies

  • #2
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I mean how do I explain the propagation of energy is discrete when I am explaining using electromagnetic wave...
With quantum field theory. Photons as particles and the description as electromagnetic waves are just different concepts, and you cannot easily combine them in a simple model.


"2." can be solved with the Poynting vector: Right
 
  • #3
Ezio3.1415
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Thanks for the reply... I think you are right about the 'right'... :D

I asked my sir the 1st question... He said that I couldn't completely visualize both at the same time(our limitation)... But he added the frequency of the photon and the alternation of the field was same(something like that)... I understand both are different concepts and quantum theory was introduced because the propagation of energy is not continuous... But there must be a link...

By the way,what does it mean by the frequency of a photon? What do we mean by that in quantum mechanics?
 
  • #4
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Both in classical fields and in quantum mechanics, you have oscillating fields associated to the electromagnetic wave, and you can look at their frequency.
 
  • #5
Ezio3.1415
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If charged particles oscillate,then the field will too and will result in emr... I am failing to view the oscillation of field with photons...
what does it mean by the frequency of a photon?

I have sort of visualized like this that the electric field and the magnetic field is alternating each other... And thus the energy is propagating... But not continuously... in discrete packets of energy 'photons'... And as the photon is 'there' because of the alternation of fields we will say its frequency would be the frequency of alternation of fields...
What do u say about it?
 
  • #6
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Think of radio waves with classical fields (many photons at the same time): You can measure the electric field direction and strength as it oscillates (for example "up" -> "down" -> "up" -> ...). And the frequency is the frequency of the electromagnetic wave.
 

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