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I Range of frequency of electromagnetic waves

  1. May 17, 2017 #1
    Theoretically speaking, does the frequency of em wave range from 0 to infinity?
     
  2. jcsd
  3. May 17, 2017 #2
    Well it can't be zero. It can approach zero, though. It also can't be infinity (being that infinity is not a real number). It can approach infinity, though.
     
  4. May 17, 2017 #3

    jedishrfu

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    I think its limited by the Planck length when you go toward 0 and limited by the size of the universe as you go toward infinity.

    https://en.wikipedia.org/wiki/Electromagnetic_spectrum

    In classical physics of the 19th century, it was believed to be continuous going from 0 to infinity.
     
  5. May 17, 2017 #4

    anorlunda

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    But Wikipedia on Plank length says that there is no proven physical significance of the Plank Length.

    Can we say that the lower (practical) limit on wavelength is the upper limit on energy? Whatever emits the photon must conserve energy.
     
  6. May 17, 2017 #5
    Do you mean that it's range is infinite from a whole numbers perspective? Because something's frequency can't literally be 'infinity'
     
  7. May 17, 2017 #6

    Drakkith

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    Whole numbers? No. Ignoring possible quantum and cosmological effects, the range includes all positive real numbers, whole or not.
     
  8. May 17, 2017 #7

    anorlunda

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    It is more of a question of semantics. Neither zero nor infinite wavelengths are practically possible. But there is no theoretically defined 0<limit or limit<infinity.

    So I think the best way to say it is that the limits are practical, not theoretical.
     
  9. May 19, 2017 #8
    If we uniformly accelerate an electron and then allow it to continue at constant velocity, the radiated E-field would seem to be unidirectional, and hence it must possess a zero frequency component.
     
  10. May 19, 2017 #9

    anorlunda

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    That's interesting. Can you tell me the difference between a zero-frequency zero-energy photon and no photon at all?
     
  11. May 20, 2017 #10
    Does a wave exist with 0 frequency? If so, should it be just a wave pulse?
     
  12. May 20, 2017 #11

    Drakkith

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    No, a wave pulse consists of many frequencies that interfere with each other to form the pulse. A wave with zero frequency can't be called a wave at all because nothing is changing. There is no oscillation, no vibration, nothing.
     
  13. May 20, 2017 #12
    Based on a picture in book 'Fundamentals of physics', wave pulse does not look like as you said. Capture.PNG
     
  14. May 20, 2017 #13
    I know topic is Em Waves and brought a picture from mechanical waves. But way of imagining even an Em wave look like this only right?
     
  15. May 20, 2017 #14
    In electronics, a "zero frequency" signal would be considered DC. So for EM, would a stationary magnet be analogous?
     
  16. May 20, 2017 #15
    Yea... the first one sounds like a wave can exist with 0 frequency (case of DC) I don't know the second.
     
  17. May 20, 2017 #16

    Drakkith

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    Sure it does. The different frequencies interfere with each other such that they sum to zero or near zero everywhere outside of the pulse.

    You can probably think of it like that, but I would still say that a wave with zero frequency isn't a wave at all.
     
  18. May 20, 2017 #17
    I agree, DC isn't a wave at all, at least not by any definition I can think of, or even just common sense. I was just pointing out a convention, or thinking that I think I've seen, that zero hertz would be thought of as DC (but no longer a 'wave'). I'm pretty sure there is a software front end for a 'wave generator' that would let you set the "frequency" to zero, and apply a DC offset.

    Would a stationary magnet be analogous to that thought?
     
  19. May 20, 2017 #18

    Drakkith

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    To a DC current? I guess you could say they are analogous in the sense that there is no change in the "signal".
     
  20. May 20, 2017 #19
    Is the frequency in electric current is caused due its patterned flow in a conductor, like in AC current, energy flow half - cycle up and then half cycle down creating to and fro motion treating as wave but not the actual frequency at which electrons vibrate when the disturbance/energy flow through conductor... Am I right anywhere? And what's the difference between a signal and a wave?
    Thanks for clarification, so there is frequency even in wave pulse.
     
  21. May 21, 2017 #20

    Drakkith

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    The details of the electric current is a bit complicated. A simple explanation is that electrons are always whizzing about in all directions and current flow is the net flow of electrons in a direction. The frequency of this net flow is the rate of the oscillation in it. The electrons themselves aren't vibrating back and forth at this frequency.

    Well, I'd say that in the context of current flow, the signal is the measurement of the voltage or current flow at any particular moment in time, regardless of its properties. The behavior of the signal can be described as wave-like when it behaves a certain way, namely that there is a repeating pattern that a wave equation can be applied to.

    That's right. Mathematically, any pulse can be broken down into the waves composing it by using a Fourier Transform.
     
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