Attention all physicists, attention

Discussion in 'General Electronics Chat' started by I have no education!, Sep 19, 2012.

  1. I have no education!

    Thread Starter Member

    Sep 19, 2012
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    QUESTION-WHY DOES THE LIGHT GO OUT WHEN YOU TURN THE LIGHTS OFF?

    On the face of it this sounds like a silly question but let me explain. Non coherent light is emitted from the light bulb when i turn the light on. Now while photons bound around the room and are absorbed and so more photons are created through the process of stimulating the atoms to release photons. In a Laser there is a process of stimulated emission by way of a lasing wavelength, now knowing this my question is under what circumstances do materials absorb photons but without the atoms being stimulated to re release a photon? Basically where does the energy of the light go if there if there is not enough light energy to stimulate the atom to release a photon again? Because if a photon is always emitted when a material absorbs a photon wouldn't light be present after one turned the light off?

    QUESTION - NEUTRALITY OF MATERIALS

    I'am aware of the laws that govern electric current and insulators and conductors and so forth. If i am say combing my hair i can transfer electrons to my hair. My question is how does say my hair or the comb or whatever regain electrons if positively charges or lose electrons if negatively charged? Like I said i'm aware of the law governing current and so obviously if i have an excess of electrons then i touch a conductor i get a shock as the electrons are transferred. But how would these additional electrons leave the negatively charged material otherwise? I read something about transferring to air molecules but was not sure about this. Or am I wrong to say that materials achieve neutrality after losing electrons and materials are constantly exchanging electrons between each other?
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    You are right!
    You have no education what so ever.
     
  3. I have no education!

    Thread Starter Member

    Sep 19, 2012
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    In what major way is my question wrong?
     
  4. MrChips

    Moderator

    Oct 2, 2009
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    The photon is absorbed by the walls and everything else in the room and converted to heat energy.
     
  5. MrChips

    Moderator

    Oct 2, 2009
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    When I buy something from you with money from my pocket I have less money and you have more. Eventually you will spend that money and I will receive some from somewhere else.
     
  6. I have no education!

    Thread Starter Member

    Sep 19, 2012
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    so materials do not seek to achieve neutrality then? It happens or it does not happen?

    Also the notion of air molecules transferring electrons is simply not something that generally occurs in the natural world?

    Thanks again for your good replies!!
     
  7. vpoko

    Member

    Jan 5, 2012
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    The law of conservation of energy says that energy is neither created nor destroyed, it's merely converted. You need to keep a few things in mind, though:

    1. Our eyes are only sensitive to a particular range of frequencies. If a photon is absorbed by something which then emits additional energy (also in the form of photons), those photons may be of a lower energy (frequency) than the original photons (for example, two photons could be emitted, each with half the energy of the original, single photon). Also, since the room is not a closed system, and the walls are not opaque to all frequencies, photons can escape.

    2. Photons are not the only way energy can be transferred. When something (say, an atom) heats up, it begins to vibrate (or rather, it was always vibrating, but the vibrations become more powerful). In addition to photon emissions (aka radiation), energy can be transferred via convection and conduction. In convection, the warm atom migrates somewhere else. In conduction, the warm atom gives some of its energy up to adjacent atoms. Again, since the room is not a closed system, energy is transferred out.

    Finally, I don't think it's a dumb question at all, though "Attention all physicists, attention" is perhaps a dumb subject ;)
     
    I have no education! likes this.
  8. I have no education!

    Thread Starter Member

    Sep 19, 2012
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    Cheers guys!!

    I knew i should have took up physics instead! Its way more interesting than electronics!! although i do get to operate in a non theoretical world!!
     
  9. I have no education!

    Thread Starter Member

    Sep 19, 2012
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    Actually wait, did Albert Einstein not have a thought experiment about what would happen to light in a room that is completely bounded by 100 reflective mirrors on all sides. I could be making this up haha, but seriously im sure i saw that somewhere. Cant remember the outcome of experiment though :confused:
     
  10. MrChips

    Moderator

    Oct 2, 2009
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    There is another simple but subtle answer. We see light because the photon interacted with your retina and gave up its energy.

    When there are no more photons to interact with your retina the lights go out.
     
  11. vpoko

    Member

    Jan 5, 2012
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    I don't know anything about Einstein postulating it (you might be right, I just have no idea either way), but you'd have to have perfect mirrors which reflect all photons and don't absorb any. The mirrors would also have to completely resist quantum tunneling (both of these are properties are not achievable in real-world materials). If you could meet those properties, then the photons would bounce around inside forever (of course you'd have no way detecting them since your detector inside the mirrors would necessarily absorb them). If you later opened a door in the mirrors, though, you'd see the light escaping.
     
  12. m1ch43l

    Member

    Aug 16, 2012
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    what?
    You're missing something here and I don't know what it is.
    The relationship you have created here for these two events is not holding water. These are two different 'machines' with different ways of triggering photon emission.
    Understand first what triggers the bulb filament to emit photons that are captured by the eye as light. Electricity (which is an event and I'm going to prove it soon) is passed through a resistive filament at a pressure (voltage). The resistive wire heats up.
    To understand this, take an analogy of a pipe that is 2m long and has been suspended between two points. The inner surface of the pipe is scarred with lumps of dirty pored metal.
    Now, switch on a powerful turbine to pump water at high pressure through the pipe. Water will face fierce resistance from the pipe's innards and will slosh within as it bumps into the bumps(This corresponds with the tungsten resistance while the water corresponds to the current. The powerful pump will provide the pressure which obviously corresponds to voltage).
    The sloshing of water leads to the pipe vibrating violently relative to its fixtures. It may vibrate to the extent of swinging about.
    This corresponds to the resistance of the tungsten relative to the current. Electrons, through friction and heat caused by this event will dislogue and do something else that dislogues photons.

    In short, a combination of extreme resistance, current, voltage and friction are responsible for the light bulb lighting when you flick the switch.
     
    Last edited: Sep 19, 2012
  13. I have no education!

    Thread Starter Member

    Sep 19, 2012
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    in reply to m1ch43l

    What are you talking about?

    is the light from a light bulb non coherent? yes

    Is stimulated emission a way of producing coherent photons in a laser? yes

    the reason for bringing these " two different machines" into the question was to demonstrate that the possibility exists , correct wavelength, that a photon can be absorbed by material and re emit another photon. So why does it get dark when i turn the lights off.

    See what vpoko has written as he knows more than i do and his explanation is most probably correct
     
  14. m1ch43l

    Member

    Aug 16, 2012
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    No they dont. If everything were neutral, God nows what would happen next. If air went neutral, how would gaseous exchange in the lungs work?
    Neutrality would occur at some point, but only briefly.
     
  15. I have no education!

    Thread Starter Member

    Sep 19, 2012
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  16. Dyslexicbloke

    Active Member

    Sep 4, 2010
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    Good point, in a room with 100% reflective surfaces you could not observe the light so it wouldn't actually matter what happened to it.
    Status quo I think ... Then again I think relativity is a basically a simple concept which almost cirtainly means I simply don't understand it in the first place.

    My head hurts, Give me a battery and a resistor any day ...
     
  17. JDT

    Well-Known Member

    Feb 12, 2009
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    Never mind the light bulb. The big question is: Why is it dark at night?

    Obvious? Think again. Google "Olbers paradox"

    (You might get some education)
     
  18. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    Photons are not emitted by materials that absorb photons. That would basically mean perpetual motion, which does not happen. You can't get free energy. When a photon is absorbed by a material, it is often changed to another form of energy, such as heat (as mentioned previously). I don't know where you get the idea that when a material absorbs a photon, it also emits one.
     
  19. vpoko

    Member

    Jan 5, 2012
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    Well, everything above absolute zero - which is to say, everything - is constantly emitting photons (black body radiation), though like you said, there's no one-to-one correlation between absorbing a photon and emitting one. A cold body in a warm environment, for example, must clearly absorb more energy (including but not limited to photons) than it emits, leading to the second law of thermodynamics. In a sense, it does cause perpetual motion, but the ability of that motion to do useful work declines as energy gradients disappear, aka entropy increases.
     
  20. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    Thank you for the correction/specification. That helps :)
     
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