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Lesson: Chapter 5 — Optics

5.1. Reflection at a plane mirror 3 of 4

The image in a plane mirror

Put a point object O in front of a plane mirror. Where does its image form, and what kind of image is it?

Rays from an object in front of a plane mirror reflecting into the eye; traced back, dashed, they meet at an image as far behind the mirror as the object is in front.

Rays from O strike the mirror and reflect into the eye. To the eye they seem to come from a point I behind the mirror, so O appears to be at I.

Virtual image

No light actually comes from the image — the rays never reach the place where it seems to be — so it cannot be caught on a screen. An image like this is a virtual image.

Properties of the image

  • Every image formed by a plane mirror is virtual.
  • The object distance (mirror to object) equals the image distance (mirror to image).
  • The image is the same size and shape as the object, and upright.