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GeoGebraGeoGebra Classroom

Image Formation in a Plane Mirror

This applet illustrates how light bouncing off an object and striking a plane mirror forms an image.
  • The mirror is the vertical blue-gray line.
  • The upright arrow on the left is an object standing in front of a mirror.
  • The solid lines show light rays bouncing off the mirror. Note the equality of incident and reflected angles.
  • The dashed lines extrapolate where light would have come from if the light traveled in straight lines (no mirror present).
  1. Move point F to see how different rays of light bouncing off the same point on the object in different directions reflect off the mirror. If your eye catches several of these rays, what common point will they all have appeared to come from?
  2. Repeat with points G and L.
  3. Based on moving these three points, where will you see the reflection of the object? Click the show image checkbox to verify your answer.
  4. Move point E to verify that the whole image will be reflected.
  5. Move F, G, and L so that the reflected rays end up at nearly the same point (your eye). How much mirror is needed to see the full image?