Snell's Law Refraction Explained

Snell's law governs how light bends, or refracts, when it passes from one medium to another. It specifically relates the angles of light rays to the properties of the media.

Snell's Law Formula

The law is expressed mathematically as:

$ \frac{\sin \theta_i}{\sin \theta_r} = \frac{n_2}{n_1} = n_{12} $

• $\theta_i$ represents the angle of incidence.
• $\theta_r$ represents the angle of refraction.
• $n_1$ is the refractive index of the initial medium.
• $n_2$ is the refractive index of the second medium.
• $n_{12}$ is the relative refractive index between the two media.

Constant Ratio Principle

For a specific colour (wavelength) of light and a defined pair of media (like air and glass), the refractive indices $n_1$ and $n_2$ are fixed physical properties. Consequently, their ratio, $n_{12}$, is also a constant value.

This means that the ratio of the sine of the angle of incidence ($\sin \theta_i$) to the sine of the angle of refraction ($\sin \theta_r$) will always yield the same constant value for that specific light colour and medium pair, regardless of the angle of incidence itself.