Ask A Scientist© Physics Archive

name        Susan
status      educator
 age         9

  Question -  1) When the light bends through the prism can we say that the red goes the fastest?

Yes, in most cases. In one particular kind of glass, fopr example, the index of refraction (c/v, where c is the speed of light in vacuum and v is the speed of a particular frequency of light in glass) is 1.514 for red light and 1.54 for blue light, so in this case the red light travels at c/1.51, and the blue light travels at c/1.54, so the red light travels 2% faster than the blue light.

Tim Mooney
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>Yes, indeed, red light is traveling faster through glass than blue
>light. Red has a smaller index of refraction than blue. Since the index
>of refraction is the speed of light in a vacuum divided by the speed of
>light in the material (in this case glass), and red refracts rotten (RRR;
>blue bends best -- BBB), red light must be going through the glass at a
>higher speed.
>
>---Nathan A. Unterman
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>since red light has the largest wavelength, it will have the largest speed
>when passing through a prism.
>Katie Page
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>Yes, blue light bends the most and red the least through a glass prism.  The
>greater bending of the blue light is a consequence of its slower speed
>through the glass;  conversely, the lesser bending of the red light results
>from its greater speed.
>
>Richard E. Barrans Jr., Ph.D.
>Assistant Director
>PG Research Foundation, Darien, Illinois
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