Physics
Explain the cause of dispersion of white light through a prism.
Spectrum
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Answer
The cause of dispersion of white light is the change in speed of light with wavelength.
When white light enters the first surface of a prism, light of different colours due to their different speeds in glass, gets deviated through different angles towards the base of the prism i.e., the dispersion (or splitting) of white light into its constituent colours takes place at the first surface of prism.
Violet colour is deviated the most and red colour the least.
Therefore, light of different colours present in white light follows different paths inside the glass prism and then strikes the second surface of prism
On the second surface of prism, only refraction takes place (from glass to air) and different colours are deviated through different angles i.e., violet is deviated the most and red the least. As a result colours get further separated on refraction at the second surface.
The light emerging out of prism, thus has different colours that spread out to form a spectrum on the screen.
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Related Questions
What do you understand by the term spectrum?
A ray of white light is passed through a glass prism and a spectrum is obtained on a screen.
(a) Name the seven colours of the spectrum in order.
(b) Do the colours have the same width in the spectrum?
(c) Which colour of the spectrum of white light deviates (i) the most? (ii) the least?
Explain briefly, with the help of a neat labelled diagram, how does white light gets dispersed by a prism. On which surface of the prism, there is both the dispersion and deviation of light, and on which surface of the prism, there is only the deviation of light?
The diagram shown below, shows the path taken by a narrow beam of yellow monochromatic light passing through an equiangular glass prism. If the yellow light is replaced by a narrow beam of white light incident at the same angle, draw another diagram to show the passage of the white light through the prism and label it to show the effect of the prism on the white light.
