| The American Heritage® Book of English Usage. |
A Practical and Authoritative Guide to Contemporary English. 1996.
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4. Science Terms: Distinctions, Restrictions, and Confusions
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| § 38. reflection / refraction |
| In everyday writing, the word refraction occurs much less frequently than reflection: They reflected on their achievements. This new theory was a reflection of her intelligence. In nature, however, the process of refraction occurs just as often as reflection. | 1 |
| Refraction and reflection describe two different options that the front of a light wave, sound wave, or any wave can take when it encounters a boundary between two media. The media can be two dissimilar substances, such as glass and air, or it can be a single substance with regions that are in different states, such as air with regions that are at different temperatures. Reflection occurs when a wavefront hits the boundary and returns to its original medium. Refraction occurs when a wavefront passes from one medium to another and deviates from a straight-line path. For example, light passing through a prism is bent when it enters the prism and again when it leaves the prism; it is, thus, refracted. Light striking a mirror bounces away from the silver backing and is reflected. | 2 |
| The boundary between the media does not have to be abrupt for reflection or refraction to occur. Consider the fact that light travels slower through air than through a vacuum, and its speed through air is dependent on the temperature of the air. On a hot day, the air directly over the surface of an asphalt road is at a higher temperature than the air further from the surface. Because the speed of light is different in these two regions, we observe an image that shimmers. This is due to refraction. A similar effect is found in the upper atmosphere of Earth at night. The “twinkling” of stars is due to temperature fluctuations in the upper atmosphere and is also an example of refraction. | 3 |
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| The American Heritage® Book of English Usage. Copyright © 1996 by Houghton Mifflin Company. All rights reserved. |
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