When light hits a smooth surface — like a mirror — it bounces off in a predictable direction. This is called reflection. We can use simple rules to predict exactly where light will go after it reflects, and to understand how mirrors form images.

1. Key Terms #

2. The Law of Reflection #

When light reflects off a surface, it follows one simple rule:

For example: if light hits a mirror at 30° from the normal, it reflects at exactly 30° on the other side of the normal.

3. Image in a Plane Mirror #

When you look into a flat (plane) mirror, you see an image. This image has three key characteristics you must know:

4. Constructions and Calculations Supplement #

4a. Drawing a Reflected Ray #

To draw the reflected ray from a plane mirror:

1. Draw the normal — a dashed line at 90° to the mirror at the point where the ray hits.
2. Measure the angle of incidence ($i$) between the incoming ray and the normal.
3. Draw the reflected ray on the other side of the normal at the same angle: $r = i$.

4b. Locating the Image #

To find where the image of an object appears in a plane mirror:

1. Draw two rays from the object to two different points on the mirror.
2. Reflect each ray using the law of reflection ($i = r$).
3. Extend the reflected rays behind the mirror using dashed lines.
4. The image is where the two dashed lines meet behind the mirror.

4c. Calculations #