Lenses

• Lenses form images by refracting light and changing its direction
• Convex lens

  • Bulges outwards
  • Causes rays of light parallel to the axis to be brought together at the principal focus
  • The principal focus is where the rays hitting the lens parallel to the axis all meet
• Concave lens

  • Caves inwards
  • It it causes parallel rays of light to spread out
  • The principal focus of a concave lens is where the rays hitting the lens parallel to the axis appear to come from
• Refraction in a convex lens

  • An incident ray parallel to the axis refracts through the lens and passes through the principal focus on the other side
  • An incident ray passing through the principal focus refracts through the lens and travels parallel to the axis
  • An incident ray passing through the centre of the lens carries on in the same direction
• Refraction in Concave Lens

  • An incident ray parallel to the axis refracts through the lens and travels in line with the principal focus
  • An incident ray passing through the lens towards the principal focus refracts through the lens and travels parallel to the axis
  • An incident ray passes through the centre of the lens carries on in the same direction