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Lenses Mirrors = “Reflection” Lenses = “Refraction”

Lenses Mirrors = “Reflection” Lenses = “Refraction”. Convex Lens (converging). Examine the outside of the eye. How many parts of the eye can you identify?. Sclera : the white, tough, outer covering Cornea : the clear covering over the front of the eye Iris : the coloured part of the eye

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Lenses Mirrors = “Reflection” Lenses = “Refraction”

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  1. Lenses • Mirrors = “Reflection” • Lenses = “Refraction”

  2. Convex Lens (converging)

  3. Examine the outside of the eye.How many parts of the eye can you identify? Sclera: the white, tough, outer covering Cornea: the clear covering over the front of the eye Iris: the coloured part of the eye Pupil: the dark oval in the middle of the iris Source: adapted from www. http://www.exploratorium.edu

  4. Make an incision in the sclera in the middle of the eye Cut around the middle of the eye You’ll end up with two halves Remove the cornea from the front half and place it on the cutting board Try cutting through the cornea – why is it so strong?

  5. Pull out the iris – it should be between the cornea and the lens, but may have stayed with the back of the eye The hole in the centre of the iris is the pupil, which lets light into the eye Remove the lens It is a clear lump about the size and shape of a squashed marble

  6. The lens feels soft on the outside and hard in the middle Hold the lens up and look through it – what do you see? Put the lens down on a newspaper and look through it at the words – what do you see?

  7. Concave Lens (diverging)

  8. Normal Eye

  9. Myopia (Short sightedness)

  10. Mirrors • Reflects light • Concave mirror = converging mirror • Convex mirror = diverging mirror • Lenses • Refracts light • Concave lens = diverging lens • Convex lens = converging lens

  11. Ray Diagrams

  12. The two important rules: • Parallel to pa → Focal point • Focal point → Parallel to pa • (pa = principal axis, the horizontal line)

  13. Convex (Converging) Lens

  14. 1. 2. 3. 4. 5.

  15. Convex (Converging) Lens

  16. Convex (converging) lenses The image will be real and invertedif the object is located further away from the principal focus. The image will be virtual, upright and enlargedifthe object is located between the lens and the principal focus. Concave (diverging) lenses Concave lenses always produce virtual images which are always upright and smaller than the object.

  17. Formulae ONE • Descartes’ Formula: • and: • m= magnification factor • h= height • d = distance from the lens

  18. Formulae TWO • Newton’s Formula: • and: • S = distance from the focal point • All distances are positive but care must be taken when calculating Sior So

  19. f is + if the lens is convex (converging) • f is − if the lens is concave (diverging) • di is + if the image is real and located on the opposite side of the lens • di is − if the image is virtual and located on the object’s side of the lens • hi is + if the image is upright/virtual • hi is − if the image is inverted/real • m > 1 if the image is enlarged

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