Electromagnetic wave peaks don't travel through space?

  • #1
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Electromagnetic wave peaks don't "travel" through space?

I'm just checking my understanding.

When a wave travels through water, you can see the peak of the wave move gradually through space.

But, it seems that an electromagnetic wave is different in that the peaks of the waves do NOT travel through space, but are instead fixed in space. For instance, by positioning food at different points in a microwave, you will find that different positions of food heat more or less depending on if the food resides where the amplitude of the wave is high.

If these waves moved 'through' space like with water, then it wouldn't matter where you position the food.

Am I correct in this understanding?
Thanks!
 

Answers and Replies

  • #2


The 'peaks' are the regions of strongest field, it's probably better to think of sound waves from a speaker than water wave peaks, you can picture the pressure waves travelling through air.
In free space the waves do travel and each point experience everthing from he maximum power through to minimum.

Microwaves are a perculiar case, because the wavelength of the radiation is relatively large, enough that only a few of them 'fit' in the oven you get standing waves so as the waves reflect off the sides not every point gets the full range of power.
This is exactly like sound waves resonating in a musical instrument or even a water wave sloshing up the sides of a bath - the wave goes up and down the sides but doesn't travel accross the surface of the bath
 
  • #3
jtbell
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Electromagnetic waves in a microwave are standing waves similar to the vibrations on a guitar string, on the surface of water confined to a bathtub, or sound waves confined to the interior of a small room.

All of these kinds of waves can also exist as traveling waves, e.g. waves on a very long string or rope, ripples spreading out on the surface of pond, sound waves spreading through open air or a large room, or electromagnetic waves spreading out from a radio tower.
 
  • #5
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Of course this is wrong:
But, it seems that an electromagnetic wave is different in that the peaks of the waves do NOT travel through space, but are instead fixed in space.

as jtbell explains.....

if the above were correct, radio transmitters, cell phones and radar, for example, would not work....
 

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