Unit 3 Properties of waves

  • A plane mirror forms an image of an object, which has these properties:
    • upright but laterally inverted i.e. the image is reversed left to right
    • the same size as the object
    • the same distance behind the mirror as the object is in front.
  • Plane mirrors are used in periscopes, security mirrors and dressing table mirrors.
  • Finding the position of the image using a plane mirror
    1. Draw any two incident rays from the object to the mirror.
    2. Draw in the reflected rays from these incident rays, making sure
      angle of incidence  =  angle of reflection.
    3. Continue these reflected rays back straight behind the mirror using a dotted line to the point where they appear to come from.
    4. The image is formed where the rays appear to come from behind the mirror. This is a virtual image. A virtual image cannot be formed on a screen. If you placed a screen at position 4 in the diagram below nothing would show. Angle on incidence and angle of reflection
  • Example
    1. An object is placed in front of a mirror. Construct a ray diagram showing where the position of the image will appear.
    2. Describe two properties of the image.
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