(a) What is dispersion of white light? What is the cause of such dispersion? Draw a diagram, to show the…
(a) What is dispersion of white light? What is the cause of such dispersion? Draw a diagram, to show the dispersion of white light by a glass prism.
(b) A glass prism is able to produce a spectrum when white light passes through it but a glass slab does not produce any spectrum. Explain why it is so.
Solution
(a) Dispersion : When white light is passed through a prism it splits into its constituent colours splitting of white light into its constituent colours is known as dispersion. Light of all wavelengths in vacuum travel with the same speed but have the different speeds in a medium due to different refractive light of indices for them. As a result different wavelength, deviate at different angle. Red colour deviates least when as violet colour deviates most.
(b) In glass slab also, dispersion takes place at AB surface, but these splitted colours emerge out in the form of a parallel beam which becomes white. A glass slab whose focus are parallel can be considered as comprising two prisms of same refractive angle. The second identical prism can be considered in an inverted position w.r.t. first prism. When a beam of white light passes from one prism it get dispersed, but on passing through the second inverted prism, the spectrum recombine to form a white light.
