CBSE Class 10 Answered

(a) White light is composed to 7 spectral colours, which are of different wavelengths. They travel with different speeds when passed through a medium like glass. As a result of difference in speeds of constituent colours of light while passing through a medium, their refractive indices are also different, and hence the white light splits into the respective spectral colours. This splitting of colours of white light is known as dispersion of white light.

(b) Range is: 4 x 10^-7 m to 8 x 10^-7 m.