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Science question. Light?
How do torches (flashlights), eyeglasses and lasers work?
Please help my assignment is due in tomorrow!
Torches using an incandescent bulb:
The electricity flowing through the filament heats it to a very high temperature so it becomes incandescent - it gives off light with a spectrum according to the black body temperature. This light is usually collected and focused to some extent by the reflector, so a beam of light is formed.
Eye glasses:
These rely on the different refraction (bending) of light by the lens (glass or plastic) and air. Rays of light passing through the lens are bent so that they can be focused on a given plane due to the curvature of the lens. The focal length can be arranged to correct for the incorrect focal length of the eyeball, so that objects come into focus at the desired distance.
Lasers:
The type we are most familiar with is a "light oscillator", so generates a beam of light. The arrangement of the light source forms an oscillator with a resonant cavity at the light emission wavelength, so that a coherent light beam is formed. This means the photons in the light beam are in phase, rather than random. They vibrate at the same rate and together. Compare with a LED, where they vibrate at the same rate (so one colour), but not together, so not coherent or in phase. Being coherent means the beam can be focused to a very small point. The output of a laser is similar to the output of a radio transmitter, but a different wavelength. The oscillation is maintained because there is optical power gain through the resonant cavity, and feedback, so a portion of the output is used to provide the input, which is amplified to become the output. Some lasers are used as amplifiers rather than oscillators.
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