# Chapter 20: Geometric Optics

**At Grade**Created by: CK-12

Light refracted through water.

Optics is the study of light. Geometric optics is the classical science of mirrors, glass, and lenses. It explains how light bends in water, and how images are formed in mirrors, telescopes, microscopes, and other devices.

- 20.1.
## Light as a Ray and the Law of Reflection

- 20.2.
## Concave and Convex Mirrors

- 20.3.
## Index of Refraction

- 20.4.
## Thin Lenses

- 20.5.
## Summary

### Chapter Summary

1. The law of reflection states that the angle of incidence is equal to the angle of reflection \begin{align*}\theta_i=\theta_r\end{align*}

The incident ray, the reflected ray and the normal are also coplanar.

2. For the object distance, \begin{align*}d_o\end{align*}

3. For spherical mirrors, \begin{align*}f=\frac{r}{2}\end{align*}

4. The lateral magnification \begin{align*}m\end{align*}

\begin{align*}m=\frac{h_i}{h_o}=-\frac{d_i}{d_o}\end{align*}

5. We define the ratio of the speed of light through vacuum \begin{align*}c\end{align*}

\begin{align*}n=\frac{c}{v}\end{align*}

Since \begin{align*}c > v\end{align*}

6. Snell’s law can be defined in terms of the indices of refraction \begin{align*}n\end{align*}

\begin{align*}n_1 \sin \theta_1=n_2 \sin \theta_2\end{align*}

The index of refraction \begin{align*}n_1\end{align*}

\begin{align*}v_2 \sin \theta_1=v_1 \sin \theta_2\end{align*}

where \begin{align*}v_1\end{align*}

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