EM radiation

  • #1
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1. How do we know EM radiation is a wave? Also, how do we know that the magnetic wave is exactly orthogonal to the electronic wave?
2. In the into to A Brief History of Time, SH says that wave-particle duality refutes determinism. How is that conclusion made?
 

Answers and Replies

  • #2
DaveC426913
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1. How do we know EM radiation is a wave?
The fact that it has a frequency/wavelength? I can demonstrate this with http://www.physics.umd.edu/icpe/newsletters/n34/marshmal.htm" [Broken].
2. In the into to A Brief History of Time, SH says that wave-particle duality refutes determinism. How is that conclusion made?
I suppose they're examining the results of two slit experiments and quantum erasers.
 
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  • #3
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The fact that it has a frequency/wavelength? I can demonstrate this in my microwave with a slice of cheese.
Just by the fact that energy is transferred to the cheese? Why does it have to be done by a wave?
 
  • #4
DaveC426913
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Just by the fact that energy is transferred to the cheese? Why does it have to be done by a wave?
http://www.physics.umd.edu/icpe/newsletters/n34/marshmal.htm" [Broken].
 
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  • #5
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So, the vertical dents will explain the E part. But what about the magnetic component? How do we know it's exactly orthogonal to the electric wave?

EDIT: actually this does not make much sense what i wrote. Maybe the dents suggest 3D waves, and maybe the origin of the beam was rotated.
 
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  • #6
BruceW
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1) The magnetic and electric fields are perpendicular because that is what they are always measured to be. The theoretical reason is simply because Maxwell's equations for a plane wave in free space say they will be perpendicular. This is for a polarised wave. For a general light wave, the electric and magnetic fields are in all directions perpendicular to the direction of the wave.
2)Collapse of the wavefunction causes it to become one of the eigenstates corresponding to the measurement made. (I.e measuring momentum causes collapse into a momentum eigenstate). But which of the eigenstates it collapses into is inherently random.
Therefore, even if you knew what the wavefunction was before measurement, you wouldn't be able to tell what the wavefunction would be after measurement. Therefore determinism is not correct, according to quantum physics.
 
  • #7
Redbelly98
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1. How do we know EM radiation is a wave?
Any EM field pattern propagates at a finite velocity, taking some time to travel over a distance. Also, the pattern of that EM field is preserved as it travels.

This can be readily seen with radio signals sent to and from space probes. The time delay in the signal is well known. That the signal pattern we send from Earth is received and understood from the space probe (and vice versa) means that the pattern is preserved.
 

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