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How light produce? and why we can see it?

  1. Nov 23, 2005 #1
    how light produce?? and why we can see it?

    why we can see light?? we can see normal visible light wave but why infared wave ??
  2. jcsd
  3. Nov 23, 2005 #2


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    I assume you mean why not infrared light.

    Our eyes are only capable of seeing visible light... its a biological thing. Many animals can see infrared however! And SOOOOOOOOOOOME people can see infrared as well... but the rest are pretty much out of our visible spectrum.
  4. Nov 23, 2005 #3


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    I don't believe that at all.

    The tiger pistol shrimp and pit viper come to mind.

    Some animals, such as bees, can also see ultraviolet wavelengths.
  5. Nov 23, 2005 #4


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    Limce87, bear in mind that the reason that the visible light part of the electromagnetic spectrum is called that is because we can see it.
  6. Nov 27, 2005 #5
  7. Nov 27, 2005 #6


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    Then you smell!

    Actually there are a very very very very incredibly rare number where people do have that capability to a small extent.
  8. Nov 28, 2005 #7
    Light is produce as electromagnetic waves . We cannot see the infrared light is because our eyes structure is build to detect a range of the electromagnetic wavelength.The electromagnetic wave which have the wavelength which is outside of these range we cannot see it because our eyes cannot detect it .
  9. Nov 28, 2005 #8
    The reason we see light is because we have special cells in our eye (rods and cones I believe) that interact with the photons we see and converts it into an electrical signal that our brain interprets and makes images out of. The reason we see only a limited range of the electromagnetic spectrum (ROYGBIV colors) is because these cells have evolved to detect this narrow range.
  10. Nov 29, 2005 #9


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    Let's just bring some reality to this. There is no hard and fast boundary between red and infra-red - it's a continuum. If you had a colour calibration card that spanned the spectrum, including IR, the farther reds would appear increasingly black.

    Normal photographic paper is particularly insensitive to red light, so much so that we can work in a darkroom under red light without the paper being exposed. As far as the paper is concerned, we are seeing light that is outside the visual spectrum. (Dumb example, I know, using an inanimate object, but...)

    Everyone's vison is slightly different. Some people are more or less sensitive to colours than others. Those who can see more into the red than others will pick up lower-freq reds slightly better. That's infra-red. Looking at the colour calibration card mentioned above, they would report total black starting further toward the end than others would.
  11. Nov 29, 2005 #10


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    What? Just when we were having so much fun calling each other names?

    Back when I was in highschool, the teacher gave one student a red rubber ball on a string and another a red rubber ball on a stick. They were, he said, an "electron on a stick" and an "electron on a string".

    The point was that since one electron repels another, the "electron on a string" would be pushed slightly from the vertical by the "electron on a stick" (which, itself, is held rigidly by the stick). If you tilt the stick slightly so that the "electron on a stick" moves closer to the "electron on a string", there is a greater force and so the "electron on a string" is pushed back more. If you tilt the stick back away, the "electron on a string swings forward. Moving the "electron on a stick" back and forth causes the "electron on a string" to move back and forth. Since the force:
    [itex]\frac{q_1q_2}{r^2}[/itex] is never 0, no matter how far apart the electrons are there will always be some force and (electrons are VERY light), some motion in response.
    But how long does this take? If an electron HERE moves, does an electron THERE move instantaneously (all relativists cringe!). When Maxwell derived his equations for the interaction of electric and magnetic fields, he showed that the could produce waves and the speed of those waved depended on such things as the "magnetic permittivity of space" and other constants that could be measured. Taking the known values for them and doing the calculation he found- the speed was precisely the measured speed of light!

    That's what light "is"- it is the interaction between electrons at far distant places in space- Across the room if I am looking at a picture on the wall, 93 million miles away if I am looking at the sun, many light years away if I am looking at a star. The reason we can "see" some of those interactions is that we have nerves in our eyes that react to the motion of electrons moving periodically with certain frequencies.
  12. Nov 29, 2005 #11
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