Concave Lens

• What should you be able to do by the end of the video on concave lenses?

  Draw a diagram showing how an image is formed by a concave lens and describe its properties
• What is the difference in thickness between the center and edges of a convex lens?


  A convex lens is thicker in the center than at the edges
• What happens to parallel rays of light when they pass through a convex lens?


  They are focused to a point called the principal focus
• What is the term for the distance from the lens to the principal focus?


  Focal length
• What is the name of the lens that is thicker at the edges than in the center?

  Concave lens
• How do concave lenses affect light rays?


  They make light rays spread out, or diverge
• What is the principal focus of a concave lens?


  It is the point from which the light rays appear to diverge
• How do you draw a ray diagram for an image produced by a concave lens?


  1. Draw a ray from the top of the object through the center of the lens without changing direction.
  2. Draw another ray from the top of the object that passes through the lens and is refracted.
  3. Draw a dotted line from the principal focus to indicate where the rays appear to come from.
  4. The intersection of these lines shows the position of the image.
• What are the three key properties of an image produced by a concave lens?


  The image is diminished, right way up, and virtual
• Why is the image produced by a concave lens considered virtual?


  Because the rays do not actually cross; they only appear to cross
• What would happen if you placed a screen where the image appears from a concave lens?


  You would not see an image on the screen
• What type of questions can you expect to find in the vision workbook related to concave lenses?

  • Questions about ray diagrams
  • Properties of images produced by concave lenses
  • Applications of concave lenses in optics
• Symbol for Concave lens