Why Can't you see Spectrum Inside a Prism?

Most recent answer: 02/10/2015

If white light falls on a prism then why is the band of colours not visible inside the prism itself?
- Roopal (age 17)
Jaipur Rajasthan India

One reason is that a good prism scatters very little light. There's almost none coming out sideways to see. Another reason is that the way a prism works is to bend the different frequencies of light slightly different amounts. Until the beam has traveled a distance quite a bit farther than its own thickness, those different directions don't show up as actual different positions of the different colors. You can see the effect here:

Light dispersion of a mercury vapor lamp

(from D-Kuru/Wikimedia Commons)

Mike W.

(published on 02/10/2015)