Lenses Mirrors = “Reflection” Lenses = “Refraction”
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Transcript of 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 coveringCornea: the clear covering over the front of the eyeIris: the coloured part of the eyePupil: the dark oval in the middle of the iris
Source: adapted from www. http://www.exploratorium.edu
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?
Make an incision in the sclera in the middle of the eye
Remove the lens
It 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 eye
The 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 middle
Hold the lens up and look through it – what do you see?
Concave Lens (diverging)
Normal Eye
Myopia (Short sightedness)
Mirrors• Reflects light• Concave mirror = converging mirror• Convex mirror = diverging mirror
Lenses • Refracts light• Concave lens = diverging lens• Convex lens = converging lens
Ray Diagrams
The two important rules:
1. Parallel to pa → Focal point
2. Focal point → Parallel to pa(pa = principal axis, the horizontal line)
Convex (Converging) Lens
Size Orientation Nature
Behind 2F
At 2F
Between 2F & F
At F
Between F & P
1. 2. 3.
4. 5.
Convex (Converging) Lens
Size Orientation Nature
Behind 2F Diminished Inverted Real
At 2F Same Inverted Real
Between 2F & F Enlarged Inverted Real
At F No image No image No image
Between F & P Enlarged Upright Virtual
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 ONE
• Descartes’ Formula:
• and:
• m = magnification factor• h = height• d = distance from the lens
oi ddf
111
o
i
o
i
d
d
h
hm
• Newton’s Formula:
• and:
• S = distance from the focal point• All distances are positive but care must be
taken when calculating Si or So
2fSS oi
f
S
S
f
h
hm i
oo
i
Formulae TWO
• 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