(a) The refractive index of glass is 1.5. What is the speed of light in glass? (Speed of light in vacuum is m s) (b) Is the speed of light in glass independent of the colour of light? If not, which of the two colours red and violet travels slower in a glass prism?
The speed of light in glass is ⁸ m/s.
Using the relation n = c/v from the textbook, where n is the refractive index, c is the speed of light in vacuum, and v is the speed of light in the medium, we get v = c/n = (⁸)/1.5 = ⁸ m/s.
No, the speed of light in glass is not independent of the colour of light.
The refractive index of glass depends on the wavelength (colour) of light. Violet light travels slower than red light in a glass prism because violet light has a higher refractive index in glass compared to red light. Since v = c/n, higher refractive index means lower speed.
Explanation
The textbook provides the fundamental relation n₂ = c/v₂, which connects refractive index to the speed of light in a medium. For part (b), the textbook discusses refraction and mentions that 'the speed of light waves is less in glass' and that 'wavelength and the speed of propagation decrease' when light enters a denser medium. The dependence of speed on colour arises because refractive index varies with wavelength—different colours experience different refractive indices, causing them to travel at different speeds through the glass prism.