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Lamps Lamps

  1. Jan 4, 2006 #1
    I have read somewhere that the usual lamps work on 3000 celsius so as to create light.. i am wondering why my lamp dont make my room to melt. Silly question eh?
     
  2. jcsd
  3. Jan 4, 2006 #2

    Danger

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    Not really. A regular incandescent bulb runs at about 2,500° C, but close enough. The heat from the filament, though, is almost exclusively transferred to the environment by radiation alone. There is virtually no conduction because there's only a very small physical connection between it and the rest of the bulb. Even so, they're obviously too hot to handle when running.
    In addition, that high temperature would quickly disperse in a greater volume of space by the inverse square law.
     
    Last edited: Jan 4, 2006
  4. Jan 4, 2006 #3

    chroot

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    If it's hot in Los Angeles, does that mean it's hot at the North Pole, too?

    - Warren
     
  5. Jan 4, 2006 #4

    Tide

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    A typical tungsten filament has a mass of only 15 milligrams so while it is very hot it contains relatively little thermal energy (heat capacity) and so can have very little impact on your substantially more massive room.
     
  6. Jan 5, 2006 #5
    Infact during the house chores of changing old bulbs I have many a times got chance to get hold of the electric bulb and also felt the heat. I use atleast a three folded cotton cloth or fold my shirt that many times to hold a bulb to be replaced which was in use till then. But 2500C is something out of my imagination. I never knew it is so hot inside.
    Anyway why won't this heat up the circuit wires. I understand the glass surface is not getting heated because it has only to face the radiation from the tungsten filament. But that is not the case od the circuit wire connected to it. They are in conduction because the connection in a bulb is directly to the filament or is it not so?
     
  7. Jan 5, 2006 #6

    Tide

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    The reason why the filament gets so hot is that its electrical resistance is relatively large due its small diameter. Yes, the wires connected to the filament also heat up but their diameters are much greater and, being excellent thermal conductors as well as electrical conductors, that heat is spread quickly through a much greater volume. The glass comprising the bulb, however, is a relatively poor conductor of heat and is close to the filament. It gets heated but cannot dissipate it as quickly as the lead wires.
     
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