Why are Waves So Long?

  • #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.
 

Answers and Replies

  • #2
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If a hertz is a cycle per second, does that really mean it's traveling 299792458 meters per second?
Yes, light travels at 299792458 meters per second.
 
  • #3
berkeman
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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.
Extremely Low Frequency RF communications is used with submarines because the low frequency RF can penetrate seawater much better than shorter wavelengths:

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

Wikipedia said:
ELF frequencies have been used in only a very few human-made communication systems. ELF waves can penetrate seawater, which makes them useful incommunication with submarines.
 
  • #4
Doc Al
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If a hertz is a cycle per second, does that really mean it's traveling 299792458 meters per second?
Realize that all electromagnetic waves travel at that speed (through vacuum), regardless of frequency.
 
  • #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?
 
  • #6
Tom.G
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without getting *Too* technical...why is it that lower frequencies can go through certain materials, but high frequency waves can't?
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)
 
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  • #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!
 
  • #8
Baluncore
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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.
 
  • #9
davenn
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Hence 2 cycles, means that it travels twice as fast...dividing that number in two.... Okay I get it, thanks guys!
no that is incorrect, the velocity of the wave didn't change
 

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