Concave lenses

• features of concave lenses

  caves inwards, thinner at centre than at edge, spreads light outwards, light appears to have come from the focal point
• how to draw the ray on concave lenses

  draw horizontal ray from top of object to lens

  draw faint line from focal point to point where ray hits lens

  the ray exits the lens along the same direction as the faint line
• what are concave lenses used for

  to spread out light further - to correct short-sightedness

  light is focused in front of the retina - needs to be spread out sightly to focus onto retina