We know from experience that a flat mirror produces an image that is the same size as the original object as well as it appears the same distance behind the mirror as the object is in front of the mirror. We can also show this using the law of reflection and ray diagrams. Using ray diagrams, you can always predict the size and location of the image that is formed in the mirror.

In the ray diagram, you will notice two light rays leaving a specific point on the object, in this case a stick figure. One ray leaves the point and hits the mirror perpendicularly. That ray bounces back from the mirror and passes back through the original point. Extend the reflected ray to a point behind the mirror where it "appears" to have come from. Then, the second ray leaves the point and goes toward a line drawn perpendicularly elsewhere on the mirror. The ray bounces off the mirror at an angle equal to the angle of incidence. The reflected ray is extended behind the mirror until it intersects with the first ray. The point of intersection between the two reflected rays behind the mirror is where the reflection of that original point would be located. Repeat this process for at least one other point on the original object to verify the full location of the image. In the example, two points at different heights on the original image were used to show that the image is flipped left to right.

There are a few key characteristics of the image formed by a flat mirror. First, the image is located behind the mirror at a distance that equal to the object distance. Second, the image is the same height as the original image. Third, the image is a reversed image. You can verify this by setting an image of a word in front of a flat mirror and seeing that the word is reversed. And last, the image is virtual. A virtual image is an image that appears to be behind the plane of the mirror and is not actually light rays converging.