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  1. J

    Stupid Light Bulbs

    I was told (in Britain) that when a bulb burned out, it was the back-emf in the coil that was responsible. Have't tried to verify this.
  2. J

    Stupid Light Bulbs

    Don't forget the changes in geometry. There may be more chance to stretch a coiled-coil into a (fat) cylinder, giving more surface area than a blob of single coil.
  3. J

    Stupid Light Bulbs

    Afterthought: maybe the coiled coil has the same temperature but greater surface area.
  4. J

    Stupid Light Bulbs

    The first part seems okay: the coil isn't at equilibrium--its inside is exposed to temperatures of around 2500 K, while its outside sees temperatures an order of magnitude lower. (The interior of the coil, being somewhat enclosed, might also have a high enough density of tungsten vapour to...
  5. J

    Stupid Light Bulbs

    A fair point, and I can't claim to have thought of it. But this seems to provide the answer: http://lamptech.co.uk/Documents/IN%20Coiling.htm Looks as though it's to do with convection in the gas. You can find complicated physics everywhere.
  6. J

    Stupid Light Bulbs

    If it was tightly coiled, wouldn't the effective area be less than this?
  7. J

    Stupid Light Bulbs

    The point (I take it) is that the calculated output doesn't match the electrical power input; the fact that room temperature isn't at absolute zero seems irrelevant: 25004 vs 3004 is a factor of nearly 5000. I don't suppose wiki specified the wattage of the bulb? Yes you might be a bit...
  8. J

    Red laser erases on glow in the dark surfaces?

    To answer your original question: Yes I'm pretty sure there is a scientific explanation. But I'm not the best person to give it. I think my original guess is reasonable: the tee shirt contains a phosphorescent dye that absorbs short-wavelength light and re-emits it slowly at longer wavelengths...
  9. J

    Red laser erases on glow in the dark surfaces?

    By "material" I meant, what were you shining the laser on? Wood, painted metal, stone, cloth? Etc.? If you leave the material in its normal state for a day or so, does it start glowing again the way it did at first?
  10. J

    Is light speed limit an artifact of the math of measurement

    A couple of thoughts after having watched the video: He's a good lecturer. He doesn't actually claim he's doing more than providing an instructive parallel to Einstein's theory. He demonstrates some of the "geometrical" features like time dilation and the combination of velocities. But he...
  11. J

    Relative Humidity (RH) affecting atmospheric attenuation of light?

    I'd be surprised if relative humidity was the key factor, unless it was so high that mist was starting to form. I think you should be asking about absolute humidity--the actual amount of water vapour in the air. Edit: There's about twice as much water vapour in the air at 50% RH and room...
  12. J

    Is light speed limit an artifact of the math of measurement

    Light doesn't behave like sound: sound is carried by the air, and the speed of sound you measure will depend on whether you are moving towards or away from the source of the sound--or, more generally, if you are moving though the air that is carrying the sound. (And of course it is possible to...
  13. J

    Red laser erases on glow in the dark surfaces?

    What was the material that was glowing? Could you tell what colour it glowed when you shone the laser on it? Was the erasure permanent? (What happened the next day?) It's possible (though it seems unlikely) that your laser was causing the glowing material to decompose chemically. It also seems...
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