There are two phenomenon at play here. And of course, towardsthe edge of a lens its shape resembles a prism.

1. When light enters s (transparent) solid, the velocity oflight in the new material will be different from that of air.You"ll have noticed a similar effect, when viewing a pencil partlyimmersed in a glass of water. You know that the pencil is straight,but it appears to bend at the water interface.

2. The velocity of light is not the same for all colours in mostsubstances.

So the different colours in the light may appear to have beenbent more than others. So the beam of white light is dispersed intoa rainbow.

A substance in which there is no velocity dispersion for thevarious frequencies of light is known as achromatic. Much thedesire of lens makers, and optical detectors.


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∙ 7y ago
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