Light
المؤلف:
GEORGE A. HOADLEY
المصدر:
ESSENTIALS OF PHYSICS
الجزء والصفحة:
p-436
2025-12-15
15
Light is the form of radiant energy which, by its effect upon the retina, excites the sensation of vision. There are many reasons for supposing that this action is a vibration of the ether. This vibration, unlike sound vibration, is transverse, - that is, perpendicular to the direction in which the light is moving.
Luminous bodies are those that emit light. The term is usually applied to those bodies only that are self-luminous. When light falls upon a body, part of it is reflected; part is absorbed by the body, changing the molecular or atomic force; and part may or may not pass through the body. Transparent bodies are those that permit light to pass through them in such a way that objects are distinctly visible through them. When light comes through a body as diffused light, and objects cannot be distinctly seen through it, the body is called translucent. If the body does not permit light to pass through at all, it is called an opaque body.
The classification of bodies as opaque and transparent is not very accurate, for thick layers of transparent bodies absorb a great deal of light, while thin layers of opaque substances are sometimes transparent.
Demonstration. - The transparency of gold leaf can readily be shown by laying a piece of gold leaf upon a glass plate and covering it with another plate of the same size. It is well to bind these together with a strip of gummed paper such as is used in making lantern slides. Hold the plates close to the eye and objects can be seen clearly through the gold leaf. Compare the color of the transmitted light with the color that is reflected from gold.
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