Lenses Mirrors = “Reflectionâ€‌ Lenses =...

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LensesMirrors = ReflectionLenses = RefractionConvex Lens (converging)

Examine the outside of the eye.How many parts of the eye can you identify?Sclera:the white, tough, outer coveringCornea: the clear covering over the front of the eyeIris: the coloured part of the eyePupil: the dark oval in the middle of the irisSource: adapted from www. http://www.exploratorium.edu

Cut around the middle of the eyeYoull end up with two halvesRemove the cornea from the front half and place it on the cutting boardTry cutting through the cornea why is it so strong?

Make an incision in the sclera in the middle of the eye

Remove the lensIt is a clear lump about the size and shape of a squashed marble

Pull out the iris it should be between the cornea and the lens, but may have stayed with the back of the eyeThe hole in the centre of the iris is the pupil, which lets light into the eye

Put the lens down on a newspaper and look through it at the words what do you see?

The lens feels soft on the outside and hard in the middleHold the lens up and look through it what do you see?

Concave Lens (diverging)

Normal Eye

Myopia (Short sightedness)

MirrorsReflects lightConcave mirror = converging mirrorConvex mirror = diverging mirrorLenses Refracts lightConcave lens = diverging lensConvex lens = converging lensRay DiagramsThe two important rules:Parallel to pa Focal pointFocal point Parallel to pa(pa = principal axis, the horizontal line)

Convex (Converging) LensSizeOrientationNatureBehind 2FAt 2FBetween 2F & FAt FBetween F & P (Converging) LensSizeOrientationNatureBehind 2FDiminishedInvertedRealAt 2FSameInvertedRealBetween 2F & FEnlargedInvertedRealAt FNo imageNo imageNo imageBetween F & PEnlargedUprightVirtual

Convex (converging) lensesThe image will be real and inverted if the object is located further away from the principal focus.The image will be virtual, upright and enlarged if the object is located between the lens and the principal focus.Concave (diverging) lensesConcave lenses always produce virtual images which are always upright and smaller than the object.Formulae ONEDescartes Formula:


m = magnification factorh = heightd = distance from the lens

Newtons Formula:


S = distance from the focal pointAll distances are positive but care must be taken when calculating Si or So

Formulae TWOf 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 lensdi is if the image is virtual and located on the objects side of the lenshi is + if the image is upright/virtualhi is if the image is inverted/realm > 1 if the image is enlarged