Question

Why does the wavelength of light decrease when it passes from vacuum into a medium? State which attributes change and which stay the same and, thus, require the wavelength to decrease.

Short answer

The speed of light decreases with the wavelength while the frequency remains constant.

Step-by-step solution

Concept Introduction

The distance between the two subsequent crests or troughs of the light wave is the wavelength of light.

When a light wave travels from one medium to another its frequency always remains the same despite changes in the speed and wavelength.

Explanation

The speed of light reduces as it moves from vacuum to medium, but the frequency of the light remains constant. Because

$\mathrm{f}=\frac{\mathrm{v}}{\mathrm{\lambda }}$

The wavelength of light, where $\mathbf{\lambda }$ is the wavelength, $\mathbf{v}$is the speed and $\mathbf{f}$is the frequency of light.

Here we can see that as soon as the speed of light decreases, the wavelength lowers to conserve the frequency of the light.