Question

White light is incident normally on a glass slab. Inside the glass slab,

• A. Red light travels faster than other colours
• B. Violet light travels faster than other colours
• C. Yellow light travels faster than other colours
• D. All colours travel with the same speed

Answer 1

The correct option is A Red light travels faster than other colours

In media like glass, different wavelengths in the electromagnetic spectrum travel at different speeds.
Refractive index ($\mu$) is related to wavelength ($\lambda$) of light as
$$\mu =A+\frac{B}{{\lambda }^2}$$
Again $\mu$ = Speed of light in Vaccum/Speed of light in medium
Hence, speed of light in media is proportional to wavelength...
Since wavelength increases from Violet to Red, Red travels the fastest.