# Understanding the spectrum of frequencies

1. May 5, 2013

### Jacobim

What is the distinction between EM waves and Sound waves.

I know that sound is cyclical vibrations in some sort of medium. When the frequency increases, do these vibrations become EM waves?

I know that EM waves do not need a physical medium. But they are still energy, and sound is energy. So do they belong on the same diagram showing freqencies?

Are sound and EM waves completely seperate things, or are they the same things but at different frequencies?

For instance, the frequency of an AC circuit. 60 hz. Does this produce a 60 hz sound wave in the air from the wire vibrating?

No it does not, be cause the thing that is oscilating is the potential in the conductor.

Is there some crossover point where energy vibrates in the EM spectrum and not in the sound spectrum?

2. May 5, 2013

### Staff: Mentor

They are no more related to one another than they are to ocean waves, or to the swaying of trees in the wind. Many different things can move back and forth for many different reasons, and the only thing they have in common is that they're waving back and forth.

No, no, and completely separate.

3. May 5, 2013

### CWatters

No. The method by which energy propagates is totally different.

I think what's confused you is that they are sometimes shown on graphs that show sound down one end and light at the other. All these scales are trying to do is show the relative frequency range they occupy HOWEVER they don't do a very good ...

For example lightning generates both sound and electromagnetic waves in the 0-10KHz range. You can hear the sound waves because the ear is designed to detect air pressure waves. You can't hear the EM waves even though they are in the same frequency band because the ear is not a radio reciever. The sound waves produced by lightning propagate a relatively short distance through the air whereas the EM waves can be detected thousands of km away.... if you have a radio reciever that convert the EM waves produced by lightning radio waves into sound waves..

http://theinspireproject.org/default.asp?contentID=1

So..

They are different things.

They can be at the same frequency or different.

4. May 22, 2013

### Jacobim

Could it be said that the eye is a radio reciever?

5. May 23, 2013

### CWatters

Only (?) in that it also detects electromagnetic waves.

I believe the detection mechanisim in the eye involves complex chemical reactions rather than purely electrical processes.

6. May 23, 2013

### phinds

No, "radio" is a specific band of the electromagnetic spectrum and the human eye does not respond to those frequencies.