Magnets and light bulb

  • #1
Guys i noticed something i can't explain, i was playing with a magnet while i was studying and my hand, where the magnet was, remained near the light bulb for some seconds, soon enough i realized that a strange sound was emitting then when i moved away my hand the emission stopped. What's the explanation? is that happening due to the photons or what?
 

Answers and Replies

  • #2
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I think it is happening because the filament or some other part of the light bulb(like maybe what is holding the filament in place) is attracted to the magnet causing there to be a strange electrical signal making you hear a strange sound. This is because while photons are directionally influenced by magnetic fields, they themselves are not attracted to the magnet so they either pass through like some of the visible light from the sun or they go to the poles of the magnet(which if they were IR photons and some of them probably are could cause your magnet to get hot which could cause you to get a burn).
 
  • #3
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You hear a sound, so it's not about photons but sound waves.
It may be that coiled filament vibrates in the magnetic field when the AC current goes through it.
The coil of a speaker works in similar conditions, in principle. You have a variable current going through a coil placed in a magnetic field.
I am not sure the effect will be strong enough in a light bulb but if you hear it.... I will try it.

What kind of magnet was in your hand?
 
  • #4
russ_watters
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What kind of light bulb was it?
 
  • #5
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I agree with nasu's possible explanation. After all, the filament is a tightly wound coil and thus creates a magnetic field of its own, which then interacts with the outside magnet's field. Since those filaments are often held in place by thin "guide rods" (for lack of a better term), I could see the filament bouncing against those guide rods, thus producing the sound.

This is because while photons are directionally influenced by magnetic fields [...] they go to the poles of the magnet

This is patently wrong. Photons do not interact with a magnetic field.
 
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  • #6
russ_watters
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My first thought was that this isn't an incandescent bulb, which is why I asked. Ballasts are electromagnetic and they hum and it would not surprise me if putting a magnet near one would (damage it) change the sound.
 
  • #7
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Oh, interesting thought, yeah. Given how incandescent bulbs are becoming less common these days, that could be it as well.
I guess I am too old-school to assume incandescent when not otherwise specified :D
 
  • #8
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Yeah, "bulb" means incandescent for my mental processor. Not even considered one of these spiral "bulbs".
They should be named something else.
I hope the OP comes back to disclose the type of "bulb" he was referring to.
 
  • #9
Greetings and thanks for the helpful answers. Actually im a student some of the things you said are kind of new to me. I'm not used to the english physics vocabulary so sometimes i consult google translate :) As you see in the image my illuminant looks some what like the one in the picture. The volume of the sound gets more intense as i go from bottom to top ( the thing in the yellow circle). the strange thing is that the Maximum volume can be achieved only if you put the magnet behind the yellow thing , i mean if you look it from the front you put the magnet behind the lamp and up it differs from lamp to lamp i assume. When i put the magnet literally on the light bulb the sound is not that sharp
 

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  • #10
The light bulb looks like this
 

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  • #11
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It looks like russ_waters' idea is more likely to be the right explanation.
It's one of these new spiral ones inside the "bulb".
 
  • #12
Ohh thank you...it was a strange phenomenon for me..
 
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  • #13
russ_watters
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  • #14
Oh, i see i was sure that the "bulb" expression was right! anyway the lamp then
 
  • #16
davenn
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Well, to an engineer who deals with lighting, a "bulb" is something that grows into a flower. A thing that you screw into a light fixture is a "lamp", reagardless of what type it is.

depends on what school you went to and what country you grew up in :wink:

in many countries ... light bulb is a pretty standard description, lamp or globe are 2 other common usages :smile:

Dave
 
  • #17
Understood, i was aware of the other 2 words as well, don't know why i choose the wrong one hehe ;)
 
  • #18
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In any case, the light bulb in question is clearly of the fluorescent type. In this case there might be some electronics integrated in the socket, and in particular a small inductance=coil. Chances are that this coil interacts with the magnetic field, causing a force that oscillates with 50 or 60 Hz (depending on your mains frequency) that
might well make the whole light bulb "sing" - as was pointed out above.

Alternatively, there might be an interaction between the magnetic field and the ionized gas within the spiral, but I think that is less likely.
 
  • #19
sophiecentaur
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Afaiaa, CFLs have a high frequency oscillator in the electronic drive circuit so the 'loudspeaker' effect could give you audible frequency sound that's higher in frequency than the mains hum. Higher frequencies would couple the sound energy into the air better than 50/60 Hz would.
 

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