Physlet Illustration: Reflection in a Plane Mirror



In this simulation, a 1-cm high object is placed in front of a plane mirror. How and where is the image formed? What are the characteristics of the image?


  1. Drag the object back and forth in front of the mirror, and study the image produced.
  2. If you click your mouse at any point along a light ray, and then drag the mouse cursor to the right along the ray, you can measure the angle of that ray with respect to a line normal to the mirror. Do so, and verify that the law of refection governs the behavior of each light ray that strikes the mirror's surface.
  3. Do the rays that leave the top of the object, traveling in different directions and reflecting off the mirror, ever come together again?
  4. Do those rays, having reflected from the mirror, appear to emanate from the same point behind the mirror?
  5. Is this, then, a real or a virtual image?
  6. The mirror is located at x = 2.0 cm. Where are the object and image located, relative to the mirror?
  7. How does the image height compare to the object's height?
  8. Is the image upright or inverted?


See Walker, Sections 26-1 and 26-2

Illustration written by Steve Mellema