Why Do Glasses and Lightbulbs Spontaneously Explode on My Desk?

[michojek]

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

RANDOMLY, seriously.. SPONTANEOUSLY they EXPLODE

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?

 

[jedishrfu]

any water dripping on them?

 

[Drakkith]

Are you playing music?

 

[Bobbywhy]

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

RANDOMLY, seriously.. SPONTANEOUSLY they EXPLODE

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?

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.

Cheers,
Bobbywhy

 

[NascentOxygen]

i leave a glass or a lightbulb on my desk

right between my screen and my speakers

RANDOMLY, seriously.. SPONTANEOUSLY they EXPLODE

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

They have not been scratched or cracked at all.

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.

 

[sophiecentaur]

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!

 

[michojek]

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

 

[A.T.]

This applies mostly to tempered glass:
http://en.wikipedia.org/wiki/Spontaneous_glass_breakage

 

[LURCH]

Is there anything in your desk under that spot? Also, was there any metal in the first piece (the one from three weeks ago)?

 

[michojek]

No there's 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

 

[mrspeedybob]

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.

 

[michojek]

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

 

[bahamagreen]

"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?

 

[michojek]

haha nope its at home,
and when it happened twice i was RIGHT THERE

just BOOM and shattered glass everywhere..
got so scared..

 

[mfb]

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?

 

[my_wan]

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.

 

[mrspeedybob]

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.

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

 

[CWatters]

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?

 

[CWatters]

Duplicate post deleted.

 

[Bobbywhy]

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

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.
http://www.batsound.com/

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.
http://audacity.sourceforge.net/

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

Cheers,
Bobbywhy

 

[jedishrfu]

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

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.
http://www.batsound.com/

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.
http://audacity.sourceforge.net/

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

Cheers,
Bobbywhy

time to get an LCD monitor and use BobbyWhy's post as justification.

 

[0xDEADBEEF]

Then there is this magic property of glass of just breaking. I find it strange that this should happen to consumer products, but if glass is not properly annealed it will look fine and after a few weeks it just breaks for no apparent reason. So you could just be unlucky with the products that you have bought, or if there is a chance that the glass got really hot and then cooled quickly (we are talking welding equipment here, not sunlight) there might be an explanation. There are methods to look for strain with polarized light, but you need special equipment. At lectures we subject large wine glasses to strong ultrasound to show the resonances. In the past they used to break, but these days the glass quality is so high that 1 cm amplitude oscillations of the rim are not enough to break them!

 

[mfb]

In the past they used to break, but these days the glass quality is so high that 1 cm amplitude oscillations of the rim are not enough to break them!

1 cm? Do you have any video of that? I would love to see that.
1cm peak-to-peak at 20kHz corresponds to ~600m/s peak velocity, about twice the speed of sound.

 

[0xDEADBEEF]

I must have a false memory then. I could be of by a factor of four or so. (If you add the opposing sides and then assume I was so impressed that it looked twice as big) Our experiment looked similar to the stronger vibrations in this one

 

[mfb]

Hmm ok, that looks more like millimeters (but it is hard to tell without scale of course), and ~600 Hz gives a lower peak velocity. Still interesting to see those large oscillations.

 

[LURCH]

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.

If you blow some smoke or mist at the lower right corner of your moniter, would that be visible?

 

[Bobbywhy]

If you blow some smoke or mist at the lower right corner of your moniter, would that be visible?

Lurch, interesting idea: visualization of an acoustic field using smoke or vapor mist! Perhaps we could see that ultrasonic sound field with some smoke/mist along with the correct illumination!

Just to amplify (pun intended) the acoustic “hum” emanating from the CRT monitor mentioned in post #20: “If the monitor was malfunctioning it would emit ultrasound.”

This failure mode occurs when a deflection coil becomes physically loosened. Originally these coils are glued or epoxied in place around the glass CRT. Over time they become loose and that’s when this problem begins. Magnetostriction is the likely source of vibration, where the deflection coils change shape minutely by extension and contraction when exposed to adjacent magnetic fields. The intensity of the fields, and thus the "hum" intensity, is proportional to the applied voltage. Because the magnetic flux density is strongest twice every electrical cycle, the fundamental "hum" frequency will be twice the electrical frequency. Additional odd harmonics above the driving frequency will be generated owing to the non-linear behavior of the magnetic materials involved. Each different harmonic contributes to the total acoustic energy emitted.

Cheers,
Bobbywhy

 

[mfb]

Quick question: You are all assuming that michojek uses a CRT monitor? They are quite rare today.

 

[Bobbywhy]

Yes, all my proposals are based on the OP's monitor being a VDU with a CRT. They are actually not rare in the world community. If the OP would specify the type of monitor he has it would be useful to solving the mystery.

Cheers,
Bobbywhy

 

[michojek]

lol its an LED.

but funny, i actually got it repaired a month ago.. because of power failure..

ist this 'leaking frequency' a health hazard?

 

[NascentOxygen]

lol its an LED.

but funny, i actually got it repaired a month ago.. because of power failure..

ist this 'leaking frequency' a health hazard?

Maybe—if you're a bat.

 

[A.T.]

Quick question: You are all assuming that michojek uses a CRT monitor? They are quite rare today.

Delaminated transformers make high pitched noises. Eventually ultra sound? Might there be one in the speakers or even in a non-CRT monitor? But quite frankly I doubt this could cause glass to break.

 

[NascentOxygen]

Delaminated transformers make high pitched noises. Eventually ultra sound? Might there be one in the speakers or even in a non-CRT monitor? But quite frankly I doubt this could cause glass to break.

Ferrite cores as used in high-frequency switching power supplies exhibit magnetostriction, so can be a generator of high-pitched sound.

 

[sophiecentaur]

How often did this happen?