How come you can't burn anything with light
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How come you can't burn anything with light

[From: ] [author: ] [Date: 11-05-24] [Hit: ]
they cant burn anything?http://en.wikipedia.The light rays leave the Sun in all directions. The distance from the sun to the earth is approximately 150 million kilometers. The light rays shining on 1 square meter are almost parallel.......
When using a magnifying glass, how come you can burn objects by magnifying the Suns' rays into a tiny dot. However, when you magnify a light bulb's light rays to a dot, they can't burn anything?

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When using a magnifying glass, how come you can burn objects by magnifying the Suns' rays into a tiny dot. However, when you magnify a light bulb's light rays to a dot, they can't burn anything?

http://en.wikipedia.org/wiki/Astronomica…

The light rays leave the Sun in all directions. The distance from the sun to the earth is approximately 150 million kilometers. The light rays shining on 1 square meter are almost parallel. Parallel rays are refracted to the focal point of the lens. This means the energy of all rays passing through the magnifying glass is focused on one tiny circular dot. When this much energy is received by a piece of paper, the paper dehydrates quickly and then ignites.

The light from a 100 watt light bulb is also shining is all directions. Since the magnifying glass is only a few centimeters from the center of the light bulb, only a tiny fraction of the light rays are almost parallel to the principal axis of the lens. So only a tiny fraction of the total energy is focused on one tiny circular dot.

Less energy on dot, means lower temperature of paper at the dot. So, no ignition, no burning!

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You can't magnify a light bulb's rays to a dot. The best you can do is a focused image of the filament or the bulb. Sun rays are parallel, and even the dot is a compromise because infrared is going to be above the dot and ultraviolet is going to be below. Sun rays are also more intense. Usually about 1,000 W per Square meter.

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It is heat (infrared radiation) that you are concentrating, when focussing (visible) light to a small area.
If it were not for the visible light, you would not even see the "dot".
That "dot" is a tiny image of the sun. It is so distant from us, it appears more like a "point" source of heat (and light).
You don't get much infrared emitted by even incandescent bulbs, and the "image" is the bulb filament, which is very large compared to the sun's image.
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