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Amazing phenomenon with glass

  1. Sep 4, 2012 #1
    I'm not sure how to put it,

    but recently its been happening, so far around 3 times,

    i leave a glass or a lightbulb on my desk

    right between my screen and my speakers


    They have NOT been exposed to mechanical stress or even rough temperatures,

    They have not been scratched or cracked at all.

    scared the crap outta me....

    any reasons or ideas?
  2. jcsd
  3. Sep 4, 2012 #2


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    any water dripping on them?
  4. Sep 4, 2012 #3


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    Are you playing music?
  5. Sep 4, 2012 #4


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    michojek, A big Welcome to Physics Forums!

    You've described around 3 events of an "exploding glass or lightbulb on my desk right between my screen and my speakers".

    With only this information one can only guess and speculate about what happened, which is not useful. We would need more specific details to generate some theory to explain what happened on your desk.

    So, will you please select one incident and describe it in clear detail. Say what you placed and exactly where you placed it. Say if your speakers were playing music (if so, loud or not). Was the object midway between the speakers? If it was the lightbulb, was the bulb lying on the desk, or was it screwed into some lamp socket? Was the lightbulb turned on?
    If it was the glass, what type of glass? Was it empty?

    Post as many details as possible and our members will do their best to explain what happened.

  6. Sep 5, 2012 #5


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    A glass—as in a drinking vessel? These would have scratches galore if they have been used and washed, and probably come with plenty of stresses from their manufacture, too. Not that any of this may be relevant to your situation, but can't be ruled out on the basis that they don't exist.
  7. Sep 5, 2012 #6


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    At what sort of level do you play your music? If it's enough to be cracking glass, then I hate to think what it's doing to your ears!
  8. Sep 5, 2012 #7
    Sorry if i didn't explain clearly enough..
    Its my first post :P

    No music (no i do not pump music and it did not happen when the music was on) and
    No water

    I placed on the bottom right of my screen which is next to one of the speakers (not the subwoofer). Speakers were NOT facing the glass.

    It was a glass casing enclosure for a lamp * you know those circular flat glasses
    and that one broke RANDOMLY 3 weeks ago.

    Suddenly today a small lightbulb i put there also broke.

    These were NOT attached to the lamp, they were just put there separately as parts..
    They were obviously not connected to the circuit *as the lamp itself was somewhere else and they were just spare parts i put there..

    They are not exposed to the sun, heat, stress, or electricity.

    I usually won't post randomly on forums, but seriously there was NO EXPLAINATION that i could come up with for this.. *and I do have SOME physics background
  9. Sep 5, 2012 #8


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  10. Sep 5, 2012 #9


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    Is there anything in your desk under that spot? Also, was there any metal in the first piece (the one from three weeks ago)?
  11. Sep 5, 2012 #10
    No theres nothing under the desk, and no the one from week 3 was just pure glass,
    the other one from today was a light bulb.

    And also I looked at the link, but i don't think lightbulbs are tempered...

    this really is a mystery :P
  12. Sep 5, 2012 #11
    Some monitors produce an ultrasonic hum. It may be that the glass is resonating with the sound made by your monitor causing it to break. It may also be that your monitor is malfunctioning causing the hum to be of higher intensity then it should.
  13. Sep 5, 2012 #12
    Wow, but doesn't it have to *ring at the right frequency?

    and also i think the glass and the light bulb are different type of glass hence

    would need different frequency
  14. Sep 5, 2012 #13
    "i leave a glass or a lightbulb on my desk..."

    I take it that means you have observed the resulting broken glass, but you have not been there to actually see this happen, right?

    Can you eliminate mischievous co-workers, angry girlfriends, and evil boss as possibilites?
  15. Sep 6, 2012 #14
    haha nope its at home,
    and when it happened twice i was RIGHT THERE

    just BOOM and shattered glass everywhere..
    got so scared..
  16. Sep 6, 2012 #15


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    Do you have any source of vibrations attached to your desk? A computer, maybe with some imbalance in a ventilator or whatever else?
    Do you have any light source close to the position of the glass?
  17. Sep 6, 2012 #16
    Best thing to do is some experiments. Place another bulb there to see what happens. Be sure to test for any unusual temperature changes in the glass. Stick your computer microphone into the region and see if it outputs noise. Perhaps there are some discharges from the monitor and such.

    Basically whatever it is you are the one with the capacity to actually test for the same and related unusual circumstances. See how many more clues you can find and we can speculate with more knowledge. No testing means no answers regardless of how rational some hypothesis may sound.
  18. Sep 6, 2012 #17
    Agreed. Leave a bulb there with everything turned off. If it does not break after some period of time turn on the computer but leave the monitor and peripherals off. Power things up one at a time until the bulb breaks. Then to confirm turn everything on except the suspect device and leave a bulb there until it either breaks or you are confident that it would have if the cause were current
  19. Sep 7, 2012 #18


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    How thick was the glass? It can vary a lot for light bulbs. Was it a normal household bulb or a quartz bulb or?

    I very much doubt it was anything to do with resonance - did any of you see myth busters try to break a wine glass using amplified human voice? The power needed was very high.

    I think more likely there was somthing like a grain of sand on the desk that caused a scratch or similar in the glass?
  20. Sep 7, 2012 #19


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    Duplicate post deleted.
  21. Sep 7, 2012 #20


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    In my opinion, the cause of the breaking of glass is ultrasonic acoustic energy coming from your monitor, just as mrspeedybob proposed in post #11. It is certainly true, as mrspeedybob also pointed out, that when the monitor is malfunctioning it emits high amplitude frequencies in the range 15-35 kHz.

    Here is a description of how your monitor operates:
    “The typical Video Display Unit (VDU) creates images in a large evacuated cathode-ray tube (CRT) by directing a beam of high-energy electrons from the cathode onto a special phosphor-coated, glass screen. This coating emits light when struck by the fast-moving electrons. The electron beam creates the image from computer signals that control coils, at the back of the CRT, that sweep the electrons in the vertical and horizontal directions. These coils are called vertical and horizontal deflection coils. The horizontal deflection coils emit fields operating predominantly in the frequency range 15-35 kHz. The electronic circuitry used to create the image gives rise to static electric and magnetic fields, as well as low and high frequency electromagnetic fields.”
    https://apps.who.int/inf-fs/en/fact201.html [Broken]

    There are at least three ways to verify this. There are instruments that detect ultrasound and down-convert into audible frequencies for use in studying bats. You could purchase one, and simply “listen” to the ambient sound around your monitor, record it, and then analyze it. This would allow the measurment of the acoustic power being radiated in the area. One source of these is Pettersson Elektronik, Manufacturer of bat detectors (ultrasound detectors) and sound analysis software.

    A second way to measure the acoustic emissions from your monitor is to download a free program called “Audacity”. Install it on your computer, connect a microphone to your computer, and record a few minutes using the program. Ordinary microphones are often sensitive to frequencies in the range of interest, especially those using piezoelectric transducers. Then display and measure the results and determine if your monitor is causing the problem.

    A third option is to swap out your monitor with a different one and see if the problem goes away.

    Last edited by a moderator: May 6, 2017
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