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  1. 05 Mar '09 16:10
    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 think, was that God created light with a thought and man creates meaningless babble with ease--but that's not my question. I want to know if he is correct about the sound-to-light comment?
  2. Standard member sonhouse
    Fast and Curious
    05 Mar '09 16:52 / 2 edits
    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?
  3. 05 Mar '09 17:57
    If the criterion is that the sound should be audible by the human ear then it's a lot "easier" to make light; any object radiates light constantly through thermal radiation.
  4. Standard member sonhouse
    Fast and Curious
    05 Mar '09 18:11
    So a search turned up one answer for light: 1.7E-17 joules makes a visible flash of light. Inverting that makes that about 6 E16 # of photons of red to make a visible flash. Now we figured 20 microwatts is about the same as 1.7E26 photons of red light so dividing the two says it takes literally billions of times less energy than my motor thought experiment. I am getting too sleepy to go further, work midnight shift and should have been in bed an hour ago! But we can see the amount of energy to be visible is extremely small!
  5. 05 Mar '09 19:55
    Originally posted by sonhouse
    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 t ...[text shortened]... an we hear a sound with less energy that a microwatt? If so, how little energy can you use?
    ….I don't think you can see just one photon,
    ..…


    Correct -and you need a minimum of TWO photon hitting the same rod cell on a retina at the same time for that rod cell to respond.
  6. 05 Mar '09 21:03
    It doesn't take much for a preacher to babble, but make him glow demands quite an amount of energy.
  7. Standard member Surtism
    Prof.
    06 Mar '09 01:33
    Originally posted by FabianFnas
    It doesn't take much for a preacher to babble, but make him glow demands quite an amount of energy.
    Or fire - then the Preacher glows for hours!
  8. 06 Mar '09 03:19
    Sound. All we have to do is talk. Walking across the room to get a flashlight or match takes more effort.
  9. Standard member DeepThought
    Losing the Thread
    06 Mar '09 05:55 / 3 edits
    You can make a sound by clapping your hands together, unless you are a glow worm, it takes a certain amount of technology to make light - as you need to start a fire or have a power station or whatever,

    This is total nonsense. It´s poorly understood science used to justify a religious argument like in the thread about ID. Although what is true is that audible sound is on an energy scale far lower than visible light. This is because visible light corresponds to atomic transition energies, whereas sound happens on a much larger distance scale (and hence lower energy scale).

    A quantum of sound in a crystal lattice is known as a phonon. Let´s compare the energy of a phonon with that of a photon. Using Planck´s formula we have E = hf where h is Planck´s constant and f is the frequency. So to compare the energy of a photon and a phonon it is enough to compare their frequencies. Visible light has a wavelength of 635nm (from memory) this corresponds to a frequency of about 50,000 GigaHertz. Audible sound has frequencies in the range 300 to a few tens of thousands of Hertz, so a single photon of visible light has an energy about 10 orders of magnitude higher than a single phonon.

    However, your eye is sensitive to single photons (*). Your ear is simply not sensitive to a single phonon. In order to hear anything you need a very large number of phonons. In fact you need a macroscopic effect. The number of molecules involved is of the order of 1.0E+23 (1 mole), so you are going to need a huge number of phonons to make something audible. Using this fairly hand waving argument I would estimate that the total energy required to make something audible is higher than to make something visible.

    (*) Having read Andrew Hamilton´s post: To get the nerve to fire you need more, but you are still looking at single figures. To hear something you need to be able to move the hairs in your inner ear around - much more energy.
  10. Standard member sonhouse
    Fast and Curious
    07 Mar '09 13:03
    Originally posted by DeepThought
    You can make a sound by clapping your hands together, unless you are a glow worm, it takes a certain amount of technology to make light - as you need to start a fire or have a power station or whatever,

    This is total nonsense. It´s poorly understood science used to justify a religious argument like in the thread about ID. Although what is true is tha ...[text shortened]... ear something you need to be able to move the hairs in your inner ear around - much more energy.
    One thing you said, visible light at 635 Nm, red, has a freq. of 50,000 GHz, or 50 Thz. That is off by almost an order of magnitude. I work in the optical industry, I am in the final test department of a laser modulator, very high tech stuff, frequency jumping and locking laser frequencies, 160 channels, and the wavelength is about 1550 nm, a much longer wavelength, more than twice the red, but we use among other instruments, an optical frequency meter and 1550 Nm comes out to 193 Thz, or 193,000 Ghz. The actual frequency of 635 nm would be the ratio of that, 2.44X that 193 Thz or about 470,000 Ghz, almost an order of mag higher than your #.
  11. Standard member DeepThought
    Losing the Thread
    07 Mar '09 15:29 / 1 edit
    Originally posted by sonhouse
    One thing you said, visible light at 635 Nm, red, has a freq. of 50,000 GHz, or 50 Thz. That is off by almost an order of magnitude. I work in the optical industry, I am in the final test department of a laser modulator, very high tech stuff, frequency jumping and locking laser frequencies, 160 channels, and the wavelength is about 1550 nm, a much longer wa ...[text shortened]... tio of that, 2.44X that 193 Thz or about 470,000 Ghz, almost an order of mag higher than your #.
    Just checked, you are right - I did something half-witted with the calculator that comes with linux. Although it doesn´t change my basic argument.
  12. Standard member DeepThought
    Losing the Thread
    07 Mar '09 17:40 / 2 edits
    Originally posted by sonhouse
    One thing you said, visible light at 635 Nm, red, has a freq. of 50,000 GHz, or 50 Thz. That is off by almost an order of magnitude. I work in the optical industry, I am in the final test department of a laser modulator, very high tech stuff, frequency jumping and locking laser frequencies, 160 channels, and the wavelength is about 1550 nm, a much longer wa ...[text shortened]... tio of that, 2.44X that 193 Thz or about 470,000 Ghz, almost an order of mag higher than your #.
    Now I´ve read your earlier post, it´s long and seemed to be talking about electric motors so I didn´t read it properly. my argument seems to be identical to yours.

    We can probably estimate the amount of energy in threshold audible sound. The figure for audibility I got from Wikipedia (http://en.wikipedia.org/wiki/Absolute_threshold_of_hearing) is 20 microPascals at 1 kHz. I couldn´t find a figure for the volume of the inner ear so I´m guessing 1 cubic milimeter = 1,0E-9 m³ Using pressure times volume to get an energy we get 2.0 E -14 Joules. This figure is nowhere near precise, it just gives us an idea of the energy scale - it ignores too much of the actual mechanics to be reliable and could be several orders of magnitude out, but it´s good enough for this. Compared with your figure for the energy of a photon in Joules (1.2 E-32) we still have an energy scale about 18 orders of magnitude greater.

    Edit: PS - I´m wondering where I got that figure of 635nm from, since you work in that field you might know, is it a particular transition?
  13. Standard member sonhouse
    Fast and Curious
    08 Mar '09 04:54
    Originally posted by DeepThought
    You can make a sound by clapping your hands together, unless you are a glow worm, it takes a certain amount of technology to make light - as you need to start a fire or have a power station or whatever,

    This is total nonsense. It´s poorly understood science used to justify a religious argument like in the thread about ID. Although what is true is tha ...[text shortened]... ear something you need to be able to move the hairs in your inner ear around - much more energy.
    According to one source I googled, retina's take 2E-17 joules to respond. The energy of one of those famous 635 jobs is about 1E-31 joules, so do the math, it takes about 1E16 of those photons to add up to 2E-17 joules. a LOT more than a couple of stray photons hitting the same retina cell.
  14. Standard member DeepThought
    Losing the Thread
    08 Mar '09 06:44
    Originally posted by sonhouse
    According to one source I googled, retina's take 2E-17 joules to respond. The energy of one of those famous 635 jobs is about 1E-31 joules, so do the math, it takes about 1E16 of those photons to add up to 2E-17 joules. a LOT more than a couple of stray photons hitting the same retina cell.
    This contradicts what is on the Wikipedia page on rod cells - what´s your reference? The rod cell being sensitive to single photons doesn´t mean a signal gets to the brain. Also the threshold sensitivity depends on ambient lighting - photo-receptor threshold intensity drops with ambient light intensity. The figure you found may refer to daylight vision rather than night vision. I can´t check the wiki reference due to it being a text book.
  15. Standard member sonhouse
    Fast and Curious
    08 Mar '09 11:42 / 2 edits
    Originally posted by DeepThought
    This contradicts what is on the Wikipedia page on rod cells - what´s your reference? The rod cell being sensitive to single photons doesn´t mean a signal gets to the brain. Also the threshold sensitivity depends on ambient lighting - photo-receptor threshold intensity drops with ambient light intensity. The figure you found may refer to daylight vision rather than night vision. I can´t check the wiki reference due to it being a text book.
    I took that quote to mean you are in a dark room and how much energy does it take to cause a visible flash of light. There wasn't much in the way of citations though. I'll have to see where I saw that one. I couldn't find the 2E-17 reference but did find this one, first talks about light in terms of electron volts then has a conversion chart at the end.
    http://www.phys.ksu.edu/gene/f_11.html

    the energy of light in joules is hC/wavelength. The hC part I already turned into a constant, 1.98E-25 so just use that # and divide by the wavelength and you see the energy in Joules. His conversion to Ev is a bit unclear, not sure of the notation used, for instance, if he says 1024, I think he means 1x10^24 so I have to go over the math carefully to figure out his formula. So for 625 nm, it is 1.98E-25/625E-9 or 3.1E-19 joules per 625 nm wave packet and inverting that you get 3.1E18 as the # of such packets to = one joule of energy.