Ultraviolet Light
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Wavelength: 10^-9m to 3.5 × 10^-7m

Sources: Ultra hot bodies, mercury vapor lamp, electric arcs (sparks).

The mercury vapor lamp works by photoelectric effect (exciting e^- in the mercury and thus releasing photons of the right frequency).

Detection: Photographic plates, fluorescence of certain chemicals, photocells, photoelectric devices.

Uses: UV light produces vitamins (in particular Vitamin D) in the skin and causes sun-tans. Note, though, that UV light is harmful even in modestly large doses. The shorter the wavelength the more dangerous the UV light is. It is used in bacteriology to kill some cells.

Comments: UV light was found shortly after infrared (early 1800s). Much of the UV light emitted by the sun is absorbed by the ozone layer in the Earth's atmosphere. Since our eyes are especially sensitive to UV light, a UV lamp should never be viewed directly. Snow-blindness, which is what skiiers suffer from when skiing on sunny areas, is caused by UV. Manufacturers of washing powders often add fluorescent powders to their products to live up to the claim that their product washes whiter than white, since these powders will absorb UV light and reradiate it as bright visible light.

Other Notes in this Category

1. Gamma Rays
2. Infra-red Light
3. Introduction
4. Microwaves
5. Radiation: properties of different types of radiation
6. Radio Waves
7. Reflection, Refraction, Total internal Reflection
8. The electromagnetic spectrum
9. Ultraviolet Light
10. Visual Light
11. X-Rays

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