• Law of reflection: Angle of incidence = angle of reflection
  • θi = θr
  • This is measured from the normal

Convex and concave mirror

Convex mirrors diverge the reflected light rays so that it appears behind the mirror.

  • The focal point is behind the mirror
  • The image is usually larger and the right way up.

Concave mirrors converge the reflected light rays so that the image appears in front of the mirror

  • The focal point is in front
  • The image is usually inverted and smaller

The same is true for waves – draw waves as wavefronts, which follow the same rules


  • An echo is a reflection of sound
  • It arrives at the listener some time after the direct sound
  • A true echo is a single reflection of the sound source
  • The time delay is the distance travelled divided by the speed of sound
  • The human brain filters out any echoes that return within 0.1 s


  • Bats, other animals and some humans have the ability to detect objects in their environment by sensing echoes from those objects.
  • Echo locators actively create sounds, e.g. by tapping or screeching
  • These sounds reflect off objects and are used by the person to accurately identify the objects’ location and size


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