Originally posted by PinkFloyd
I know--some will say this goes in Spirituality, but I don't think so, so there!
A radio preacher was saying that a professor told him that it took very little "energy" to produce an sound audible to the human ear. However, to produce just one point (I think he meant photon) of light requires an incredible amount of energy. The point of the sermon, I th ...[text shortened]... t that's not my question. I want to know if he is correct about the sound-to-light comment?
From a science perspective, forgetting about the religious aspect, my feeling is it would take more energy to make an audible sound than a visible photon. I don't think you can see just one photon, though, they can be detected and MADE visible with Avalanche diode detectors hooked to a screen or some other method of amplification but that involves devices that take energy.
But in order to make a sound, you have to vibrate something, but there is a new kind of loudspeaker that makes sound without vibration, it uses some kind of thermal effect and the speaker element does not vibrate, somehow the device, which I think is a graphene layer, those one atom thick carbon affairs heats up the air in front of the the layer somehow, so from a science standpoint, it is an interesting question.
There is a relation between the frequency, the color, of light, it takes less energy to make red than violet and less energy to make infrared, which of course is invisible but deep red that is still visible requires the least energy in our visible spectrum.
The question boils down to the basic sensitivity of the ear V the eye, how many photons does it take for the average person to recognize it as a pulse of light?.
I know I have very sensitive hearing, at least when I was in my twenties, was given a hearing test and I could hear the sounds at the lowest setting they could put the machine and then when they said the test was over, and they turned it off, I even heard the faint sound of it dying away, a signal that went to lower and lower pitches as it shut off, fainter than the lowest setting but I still heard it, so that amount of energy must have been measured in microwatts that I heard.
I did an experiment at one company I worked for where they used these micro motors for a tiny flow of air for a scientific instrument that measured air pollution, the motor had a little suction pump that pulled air into a tiny chamber and the motor was a lot smaller than the kind you see in those little slot cars. So I had a few of them on the bench and a good DVM and a very sensitive ammeter that went down to pico-amps and a variable power supply, I wanted to see what was the minimum amount of energy I could use to make that motor spin, even if slowly. It turned out it would start spinning with about 10 MICROWATTS applied!
That is a very small amount of energy and blew me away. I couldn't believe I could make that motor turn with only a few microwatts but it did.
Now you could see how you could have that motor shaft with a little pin sticking out that could just barely touch a piece of paper say, and each rev would produce a sound pulse.
There would be some minimum amount of friction added by the pin to overcome when it touches the paper but I would bet it would not need more than double the amount of power needed to just turn the shaft, so around 20 microwatts should be able to produce a sound you could hear if you were close to it.
My hearing was sensitive enough to hear bugs crawling inside logs and such when I was a kid, I could hear the little scratching sounds they were making, like maybe termites biting the wood, so you can imagine those bugs would not be generating much energy, probably less than a microwatt to do their thing but I still heard the little buggers.
I also had an ant colony when I was ten and I could clearly hear the ants scrambling around inside the tunnels which were visible because they were in thin layers of dirt with glass on both sides maybe a quarter inch apart so you could see and hear the scritching sound they made as they dug. I could anyway.
I still have much better hearing than most people even though I am closing in on 70 ( a few year left for that one anyway), I tell my wife, I wonder what that bird is, it is a block away and twittering and she goes, what bird?
I tend to think good hearing is something that you can train yourself to have, just by paying close attention to sound and concentrate on hearing.
I think most people don't pay much attention to sounds around them but I am a musician and sound goes right to my brain with no filters which can drive me up a wall when I go to a restaurant with so-called music playing, it is like root canal surgery for me!
So now I will have to do a little digging and see which sense is the most efficient energy wise, that is half the battle, then you have to figure out which form of vibration, sound or light, takes the least energy to generate, another problem entirely.
The amount of energy in a photon is easy to calculate, it's just (h*C)/wavelength now h is about 6.63 E-34 and C is 3E8 m/s so you can arrive at a useful constant by just multiplying the two together, which comes out to about 1.98 E-25. So remember that number, you don't have to do the multiplication every time to figure out the energy of photon now. A red visible light photon comes in about 600ish nanometers, so just multiply our little hc 1.98E-25 times 600E-9 and that come out to about 1.2 E-32 joules ( the answer in these units is in joules) a joule spread out over one second is one watt/second. Now if you invert that answer, you get how many photons of that frequency, red color = 1 watt or one joule, that is 8.4E30 red photons = 1 watt.
So that 10 microwatts that ran that motor would be 8.4E30/100,000 or 8.4 E 25 photons to equal 10 microwatts so lets take that number I generated that could make a sound at least with that little motor and a pin hitting a piece of paper, and that would be be about the same as 1.7 E26 red photons. Now we have to determine if you can see 1.7E26 photons. My gut feeling is you would easily see that many in a dark room at least. But you can see how the math works anyway. Not sure where to find out the energy of the lowest sound that normal people can hear, have to make a search. Can we hear a sound with less energy that a microwatt? If so, how little energy can you use?