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?


Speed of light in glass is dependent on the colour of light as different colours have different wavelengths, thus different velocities.


We know that refractive index of a material in terms of the wavelength of light is


μ = a + (b/λ2)


As the wavelength of violet light is smaller than that of red light,


μv > μr.


We also know that


Or


vv < vr


Hence velocity of violet light in glass is less than velocity of red light.


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