When white light enters a prism and splits into its constituent colours, it is due to dispersion of light caused by different refraction for different wavelengths.

Quick Scoop

One-line answer

The splitting happens because each colour in white light bends (refracts) by a different amount in the glass, so they spread out into a spectrum – a phenomenon called dispersion of light.

What is happening inside the prism?

  • White light is a mixture of many colours (red, orange, yellow, green, blue, indigo, violet), each with its own wavelength.
  • When this light enters the prism, it slows down and bends because it goes from air to glass – this bending is called refraction.
  • The refractive index of glass is slightly different for each wavelength, so each colour travels at a slightly different speed in the glass.
  • Because of that, each colour is deviated (bent) by a different angle, so they fan out and form a spectrum instead of staying together as white light.

A key detail: violet light (shortest wavelength) bends the most, and red light (longest wavelength) bends the least, which is why they appear at opposite ends of the spectrum.

If this were a multiple-choice question

For the exam-style question:

"When white light enters a prism, it gets split into its constituent colours. This is due to"

The correct option is typically:

Dispersion of light due to different refractive indices for different colours (wavelengths) in the prism material.

Tiny story to remember it

Imagine a group of runners (the colours) entering a muddy field (the prism).
They all ran together on the track (in air), but in the mud some are faster, some slower.
Because they move differently, their paths spread out, so by the time they leave the field, they are separated – just like colours coming out of the prism as a rainbow.

TL;DR:
White light splits in a prism because different colours have different wavelengths, so the glass bends each colour by a different amount – this effect is called dispersion of light.

Information gathered from public forums or data available on the internet and portrayed here.