Question

When light passes through a dispersive medium, it breaks up into various colours. Which of the following statements is correct?

• A. Velocity of light for violet is greater than velocity of light for red in dispersive medium
• B. Velocity of light for violet less than the velocity of light for red in dispersive medium
• C. Velocity of light is same for all colours in the dispersive medium
• D. Velocity of light has nothing to do with the phenomenon of dispersion

Answer 1

Answer: (B)

When white light passes through a dispersive medium say prism, it splits into its constituent colours. This is known as dispersion. The reason for dispersion is that in a material medium the light rays of different colours travel with different speeds. Hence, refractive index n is different for different colours.
$n=\frac{\text{ speed of light in vacuum }}{\text{ speed of light in medium }}$
In glass speed of violet light is minimum while that of red light is maximum.