Assumption: Light travels in straight lines
A light ray is a line in the direction along which the light energy is flowing.
Multiple rays from the point P reflect from the mirror. Each ray obeys the law of reflection: the angle of reflection equals the angle of incidence.
An image is formed at point P'. The reflected ray seems to have traveled from the point P', tracing the reflected ray backward through path "inside the mirror."
The image created is called a virtual image, since it cannot be seen on a screen. We define the distance s from the point P to the mirror. We define the distance s' as the apparent distance from the mirror to the image, or the "image distance."
For a flat mirror, the distance s' = s.
For a flat mirror, the image size is the same as the object size. The magnification, m = 1.
Your eye detects the rays which seem to be diverging from the point source P'. The lens in your eye causes the rays to converge and focus on your retina.
Two plane mirrors form a right angle. How many images of the ball can you see in the mirrors from this position?
You are standing a distance s from a mirror, looking at the reflection of your toes. How far is it from your eyes to the point of reflection s’, if your eyes are a distance D from the floor?
If your height is h and your eyes are l1 from the top of your head, what is the shortest mirror on the wall in which you can see your full height? Where must the top of the mirror be?