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Do we know what radio waves look like?

  1. Dec 17, 2014 #1
    A thought occurred to me In precalculus class. At the moment we are learning about sin/cos/tan/cot/sec/csc and their amplitude, periods and phases shifts. I've studied electronics on and off for about a year. I would like to know if we actually know what radio waves look like? do they actually look like the sine and cosines like in mathematics textbooks. Or are those wave functions just representations of something we can't see be can only analyze their effects. And therefore something we don't know what they look like.

    Please explain

    Thank you
     
  2. jcsd
  3. Dec 17, 2014 #2

    jtbell

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    Do you mean radio waves that are carrying signals, e.g. music? Look up "amplitude modulation" and "frequency modulation".
     
  4. Dec 17, 2014 #3

    nsaspook

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    When we detect the waves from real transmitters using receivers moving in space they behave exactly the same as the mathematical models predict.

     
  5. Dec 17, 2014 #4

    davenn

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    nsaspook, that's an interesting experiment / demonstration :)

    Dave
     
  6. Dec 18, 2014 #5
    Davenn I think what nsaspook is getting at Is that any time we measure an em wave, it is only measured by its effects on matter (*). Even when we see light, it's because our eyes have matter in them that is designed to react to the light. You might want to look into ether theory, which is an outdated theory that em waves propagate through a material that we don't see.

    Here's a question that might be worth considering, is an em wave anything more than the mathematical description of its effects? And if we have no description for its effects when matter isn't involved, is it even sensible to talk about what it looks like when not interacting?

    (*)light waves do interact with themselves, but again we can only measure this by their interaction with matter.
     
  7. Dec 18, 2014 #6

    davenn

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    why do you think I have a problem with the video ??
    I didn't state that, you are not telling me anything new , your post is irrelevant ;)
     
  8. Dec 18, 2014 #7

    sophiecentaur

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    You seem to have got it more or less right here. You can't "see" EM waves (except the visible wavelengths) but you can plot graphs which show how the E and H fields vary in time and space. In the same way, we cannot 'see' the way the daily temperatures in your house vary - or prices on the stock exchange - but we are all happy to draw and read graphs that show the variations. Radio waves don't 'look like' anything - no problem. Our brains and culture have allowed us to appreciate variations graphically (a brilliant ability) and even the least mathematically adept person can appreciate hand waving and crude graphs on paper.
    Many but not all EM waves have sinusoidal variations and that's how they are often drawn but a continuous sine wave doesn't carry much information (limited to "transmitter is turned on"). When a radio wave is Modulated (AM / FM / Digital) it carries information as it is varied in amplitude, waggled about in frequency or pulsed with digits; that is the information that it carries. The waveform can be very complex. One thing that's always important to realise is that there is no actual movement or 'side-to side wiggling' involved. The wiggles on the drawings you see just represent the amplitudes of the fields. I often think that approaching EM from the direction of Light Frequencies is harder because people always want to introduce Photons onto the scene and they introduce as many problems as they solve. You can stick with radio frequencies to understand most (all) of the classical approach to EM.
     
  9. Dec 18, 2014 #8
    Haha alright. I didn't have access to YouTube at the time unfortunately. Darn work website blockers.
     
  10. Dec 18, 2014 #9

    sophiecentaur

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    I wasn't all that impressed by the video. It seemed to be a compilation of all the stock diagrams with a commentary that was spoken too fast. They seemed to know all the necessary bits but didn't seem to be putting any special take on the subject. Imo, people are losing the ability or preparedness to read some pages from a text book and figure out for themselves what the book is trying to say. When you think how much time and effort has been taken to present the ideas in a good text book, it's really worth trying it the 'old fashioned' way.
     
  11. Dec 18, 2014 #10

    sophiecentaur

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    It worries me that the OP hasn't come back to the thread. That implies we are responding in the wrong way for him / her.
     
  12. Dec 18, 2014 #11
    @sophiecentaur No no no I am here, just sifting through other posts as usual. I'll often have have many different pages open at once. I think I get the general idea of this though.

    To all. How exactly do we see/measure the effects of radio waves to know they are there? what effect does it have on matter
     
  13. Dec 18, 2014 #12

    Drakkith

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    They cause charged particles to move. For example, radio waves will exert an alternating force on the charges in an antenna, which we see as AC voltage.
     
  14. Dec 18, 2014 #13

    sophiecentaur

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    Hi. Nice to know we are not arguing into a vacuum. :)
    We can 'know' that waves are there by using sensors and receivers. RF waves affect matter by causing currents (electrons) to flow in antennae and RF amplifier / detectors. We can actually 'look' at Oscilloscope traces of the actual waveforms of signals up to many GHz frequency. It is much harder (and it used to be impossible) to look at the actual waveforms when dealing with light. But in laser light, despite being formed by the emission from many different atoms, can have photons that are, in synchronism with each other. We can know the waves are there using photo detectors (diodes and photoelectric cells etc.) or using a laser that acts as a receiver by being triggered by the incoming light (laser amplifier) . In all this cases, though, the matter that the EM wave interacts with will be electrons. At optical frequencies and above, the photon nature of the EM is far more obvious because E = hf and the possible values of f can be very large compared with the photons of Medium Frequency Radio transmissions..
    Very high energy photons (gamma rays) will interact with the constituents of an atomic nucleus.
     
  15. Dec 20, 2014 #14

    nsaspook

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  16. Dec 20, 2014 #15

    sophiecentaur

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    Beware. Notice that the title involves "Visualisation of", which doesn't actually claim 'seeing'. It's still only a 'graph' of what's happening. (Which doesn't matter because it is still informative - but not the same thing.)
     
  17. Dec 20, 2014 #16

    nsaspook

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    True but isn't seeing a 'Visualization' using our brains and senses. All 'seeing' uses instrumentality (wetware or hardware).

    It's pretty cool that two completely different 'Visualization' devices 'see' the same thing.
     
    Last edited: Dec 20, 2014
  18. Dec 20, 2014 #17

    sophiecentaur

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    We're into semantics here. The logical answer to the OP is that we can 'see' anything, if we can be made aware of the effect it has on something. But the OP actually acknowledges that and, to be honest, answers his own question.
    In this age of image synthesis and processing, we cannot ever say 'seeing is believing'.
     
  19. Dec 20, 2014 #18

    nsaspook

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    It's been that way for a while.
    lyingeyes.jpg
     
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