lenses and the formation of images

• the two basic lens shapes
• when light passes through a lens, it is refracted twice. When does this happen?


  once on the way in, once on the way out
• what are the 2 basic lens shapes?

  converging and diverging .
• converging lens

  they are thickest in the middle and gather parallel incident light into one single point
• diverging lens

  they are thinnest in the middle and cause parallel incident light apart
• how can ray diagrams be simplified?

  by drawing a dashed vertical line through the centre
• converging lenses
• diverging lenses
• what is the centre of the lens called?

  the optical centre (O)
• light rays parallel to the principle axis will converge where?

  the focus (F) behind the lens
• what is the focus on the back side of the lens called?

  the secondary focus (F')
• where is the principle focus for diverging lenses?

  on the same side as the incident light rays