Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Why are Waves So Long?

  1. Jun 13, 2016 #1
    Hi everyone... So, I may be putting too much thought into this. But I'm studying for my Ham Radio license, and I was pondering the size of our allotted range of frequencies. The lowest frequency is in the 160 meter range (clocking in at 1.8 Mhz) So, of course I was thinking what other things use those lower ranges and what they equate to in meters. I noticed that 1 Hertz. (One cycle per second) is equal to 299792458 meters! How is this possible? And Why? If a hertz is a cycle per second, does that really mean it's traveling 299792458 meters per second?

    Also for something like low, can you possibly even modulate it to send data? To me, it feels like that wavelength is so long, that it'd be hard to actually "apply" data.
  2. jcsd
  3. Jun 13, 2016 #2
    Yes, light travels at 299792458 meters per second.
  4. Jun 13, 2016 #3


    User Avatar

    Staff: Mentor

    Extremely Low Frequency RF communications is used with submarines because the low frequency RF can penetrate seawater much better than shorter wavelengths:


  5. Jun 13, 2016 #4

    Doc Al

    User Avatar

    Staff: Mentor

    Realize that all electromagnetic waves travel at that speed (through vacuum), regardless of frequency.
  6. Jun 13, 2016 #5
    Thanks for the responses everyone....So I suppose without getting *Too* technical... why is it that lower frequencies can go through certain materials, but high frequency waves can't? What is it about the properties that make one wave good for one type of propagation? Just like how higher frequency waves are good at getting through the Ionosphere, but longer waves are pushed back down?
  7. Jun 13, 2016 #6


    User Avatar
    Science Advisor

    The 'Simple' answer is that the losses occur per cycle of the wave. Shorter wavelengths have more cycles per given distance, hence are absorbed more by, say, seawater. (Ref Post #3 by berkeman)
  8. Jun 14, 2016 #7
    I see! Thanks everyone, I never sort of combined the two pieces of knowledge that EM waves travel at the speed of light. And one hertz is the wave "Traveling" So it can travel (complete 1 cycle) once per 299792458 meters. Hence 2 cycles, means that it travels twice as fast...dividing that number in two.... Okay I get it, thanks guys!
  9. Jun 14, 2016 #8


    User Avatar
    Science Advisor

    The frequency, f, of the wave is independent of the propagation medium.
    The unit of frequency is hertz, Hz, which has the units of sec-1.
    From frequency you can calculate the wave period, T, in seconds, T = 1 / f.

    The wavelength, λ, is then the period * speed of propagation.
    Only in free space is λ = 299792458 / f.
  10. Jun 14, 2016 #9


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    no that is incorrect, the velocity of the wave didn't change
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted