Question

(a) The refractive index of glass is `1.5`. What is the speed of light in glass ? (Speed of light in vaccum is `3 xx 10^(8) ms^(-1)`).
(b) Is the speed of light in glass independent of colour of light ? If not, which of the two colours, red and violet travels slower in a glass prism ?

Answer 1

(a) Here, `mu = 1.5, v = ?, c = 3 xx 10^(8)ms^(-1)`
As `mu = ( c)/(v) :. V = ( c)/(mu) = (3 xx 10^(8))/(1.5) = 2 xx 10^(8) ms^(-1)`
(b) No, the refractive index and the speed of light in a medium depend on wavelength i.e. colour of light. We know that `mu_(v) gt mu_(r )`. Therefore `v_("voilet") lt v_("red")`. Hence voilet component of white light travels slower than the red component.