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Random sound i discovered

  1. Oct 19, 2012 #1
    hello physicsforum. i came here hopefully someone can answer this.

    heres what happend:

    i was out suing my camping stove. after i turn it off, and start packing it away, i shone the flashlight onto it and thats when i first discovered that there is a buzzing sound coming from it.

    cannot explain how or why the the buzzing sound is being made. i was able to confirm that the buzzing sound is coming from the stove.

    when i first discovered the noise, i was shining it under the stove. i went to go look closer and it stopped. tried to make it make the sound again, couldnt. waited a few minutes, then started packing it up again. by this time the stove was cold. i shone the flashlight at the top and it started making the sound again. thats when i recorded it. after i recorded it, i touched the top and it would stop making the sound.

    if you are asking, the stove is a:

    MSR whisperlite multifuel stove. basically made of stainless steel burning kerosene, so stainless steel covered in carbon


    when i first discovered it, the stove was hot, the 2nd time it was cold. the 2nd time i tried it (what you can see in the video) it looks like the sound is coming from the screw in the middle. when i touched it later, i touched it on the side. then it stopped.


    the flashlight is a Jetbeam bc25 using a cree XM-L LED


    seriously, can anyone figure out why it is making a sound. no one can figure it out.

    sorry, im just trying to be as descriptive as possible.

    the video i recorded:

    http://www.youtube.com/watch?v=5trVydyIxT4&

    cheers
     
  2. jcsd
  3. Oct 19, 2012 #2

    Drakkith

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    Whoa, crazy!
     
  4. Oct 19, 2012 #3
    Maybe the inverter in your flashlight. Try connecting headphones to a solar cell and shine the flashlight onto it. Does it make the same noise?
    What part of the stove makes the noise? The piezo igniter?
    Can a flashlight with incandescent bulb cause a noise too?
     
  5. Oct 19, 2012 #4
    i shone the flashlight at the bottom of the stove (brass tip) when it was hot. made the same sound.

    the sound seemed to come from the screw in the middle. there is no ignition on the stove. i use a lighter to light it.

    it is made of stainless steel and brass.

    i like the solar cell/headphone idea. sadly, due to camping, i do not have such equipment.


    id try it again but it is about 4am here
     
  6. Oct 19, 2012 #5

    HallsofIvy

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    My thought is that you didn't close off your gas tank securely and gas is hissing as it comes out. That would have nothing to do with shining light on it but it is possible that the noise is so low you don't notice it if you are not specifically focusing on the tank.
     
  7. Oct 19, 2012 #6

    Drakkith

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    Did you see the video? It is literally only there when the light is hitting it. The camera isn't moving.
     
  8. Oct 19, 2012 #7
    Any chance there is a bug stuck in there somewhere that gets irritated by the light? From the video it doesn't sound like a bug but I don't have any other ideas.
     
  9. Oct 19, 2012 #8

    CWatters

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    I agree with DrZoidberg. Most likely there is a stray magnetic field from the inverter in the torch causing the metal to vibrate.

    You could prove it's not the light from the torch by inserting a sheet of black card between torch and stove. I believe it will still make the noise.
     
  10. Oct 20, 2012 #9
    If it were a magnetic field, why would the sound change as the light moves around? The reflector it the flashlight would not focus the magnetic field. After contemplating this for a bit I have another suggestion.

    This flashlight may cycle the LEDs on and off at high frequency either as a side-effect of voltage regulation or it may use pulse width modulation to keep the brightness constant as the battery voltage varies. The LEDs could switch fast enough that they actually do turn on and off without your eye perceiving it. If the frequency of the light switching matches the resonate frequency of the metal the light could set up a harmonic vibration via cycling light pressure.
     
  11. Oct 20, 2012 #10

    AlephZero

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    Yes in theory, but in practice there is a (large) order-of-magnitude error in that explanation.

    A more plauslble version would be that the torch makes a sound when it is on, and the air pressure is making the top of the stove resonate.

    At that high frequency, the wavelength of the sound will be similar to the size of the torch and the stove top, so any sound from the torch may be very directional.

    Can you hear anything if you shine the torch into you ear from close range?
     
  12. Oct 20, 2012 #11

    mfb

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    What happens if you:

    - do the same as in the video, but with the flashlight turned off?
    - bringt the (active) flashlight close to the stove, but shine in a different direction?

    Maybe that, plus a thermal effect?
     
  13. Oct 20, 2012 #12

    CWatters

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    No but moving the light brings it closer/further away.

    Try putting card over the LED to block the light.
     
  14. Oct 20, 2012 #13

    sophiecentaur

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    This is a good one!!

    Have you tried different light sources?
    Have you tried putting different steel / magnetic objects near that particular torch?
    That could narrow the study down to either stove or torch.
    I agree that keeping the torch in the same place but blocking the light could increase knowledge of the system.
    What grade of stainless steel is the stove? Some grades are magnetic and others (marine grade, for instance) are not.
    Can you repeat this at home?
     
  15. Oct 20, 2012 #14
    The simplest explanation is that rankzerg is just turning on a buzzer every time the light is shone on the whisperlite. So, the first experimental control would be to make sure that you are not turning on a buzzer with your other hand:smile:
     
  16. Oct 20, 2012 #15
    I was wondering when someone would suggest the possibility of a hoax. This video could be easily reproduced using a photo-resistor controlled audio oscillator.
     
  17. Oct 21, 2012 #16
    If it is not a hoax. One of the most possible is photo-electric effect, as you mentioned that the stove is made of stainless steel and brass. The steel-brass junction converts light energy to sound or vibration. But the magnitude of the light energy is still too low. Usually we don't notice different combinations of other metal junctions with closed circuit produce sound. Does the system generate sound under sunlight or fluorescent light. Does the amplitude increase/decrease when the torch moves away or closer, or even the frequency of the sound changes ?
     
  18. Oct 21, 2012 #17

    Bobbywhy

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    "The steel-brass junction converts light energy to sound or vibration?" you say? Please provide some reference that explains this process. I've never heard of this.

    Cheers,
    Bobbywhy
     
  19. Oct 21, 2012 #18
    Thanks. It should be a junction of semi-conductors (much a lot sensitive) for photo-electric effect, and the metal-metal junctions (couples of pairing of hot and cold terminals) for converting heat to electric energy (not sure whether this process is reversible). When light shinning on metals, electrons in metals excite too. In vacuum the electrons which fly away from the metals may be attracted by some anode(= +ve voltage?) or positive plates with sufficiently higher voltage. Different metals in appropriate electrolytes similar phenomenon (reversible) also can take place but the mechanism not same. Cannot explain how these supposed electric energy (converted from light) generate sound. The idea is electrons moving -> electricity -> vibration or sound. The primary idea is there exists junction with different metals, and closed circuit.
     
  20. Oct 21, 2012 #19

    sophiecentaur

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    There is definitely something very relevant to this that we are not being told - either deliberately or through an oversight.
    The only way to sort it out, if it is genuine, is to try to reproduce the effect with various bits of the original equipment and at a different location. We can be sure that there is a rational explanation for it .
     
  21. Oct 21, 2012 #20

    CWatters

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    It's usually a mistake to consider complicated solutions when you haven't yet eliminated the simple ones.
     
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