Index of refraction

Definition

The index of refraction, or refractive index, is a dimensionless number that describes how light propagates through a medium. It is defined as the ratio of the speed of light in a vacuum to its speed in the specified medium.

5 Must Know Facts For Your Next Test

1. The index of refraction is denoted by $n$ and has no units.
2. It can be calculated using the formula $n = \frac{c}{v}$, where $c$ is the speed of light in vacuum and $v$ is the speed of light in the medium.
3. When light moves from one medium to another with different refractive indices, it changes direction according to Snell's Law: $n_1 \sin(\theta_1) = n_2 \sin(\theta_2)$.
4. A higher refractive index means that light travels more slowly in that medium compared to one with a lower refractive index.
5. Common materials have specific refractive indices, for example: air (approximately 1.0003), water (about 1.33), and glass (ranging from 1.5 to 1.9).

Review Questions

• What does the index of refraction tell us about a material?
• How do you calculate the index of refraction for a given medium?
• Explain how Snell's Law relates to the index of refraction.

Related terms

Snell's Law: A formula used to describe the relationship between angles of incidence and refraction when light passes through different media: $n_1 \sin(\theta_1) = n_2 \sin(\theta_2)$.

Total Internal Reflection: A phenomenon that occurs when light travels from a medium with a higher refractive index to one with a lower refractive index at an angle greater than the critical angle, causing all the light to be reflected back into the higher-index medium.

Critical Angle: $\theta_c$, the minimum angle of incidence at which total internal reflection occurs when moving from a medium with high refractive index to one with low refractive index.