refraction lenses(1)
TRANSCRIPT
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Refraction 2Lenses
Copyr ight Mark Jordan
Davitt College,
Castlebar
For non-commercial purposesonly.. Enjoy!
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C1 C2
C1 & C2 are the centres of the spheres of which the surfaces of thelens form a part
The line through C1 & C2 form the principal axis
Converging Lens
Principal axis
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C1 C2
Converging lens
FF
A ray of light on entering the lens is refracted towards the normal
and on leaving away from the normal. Since surfaces are inclinedtowards each other the ray is refracted towards the principal axis.
Rays parallel to the principal axis
converge towards a point called
the principal focus F.
Since light can travel equally
well in both directions, there
are two foci.
Normal
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F = Focal point
To locate the position of an image in a convex lens we use two
of the following rays of light
FF
3 through the focus emerging parallel to principal axis.
1 parallel to the principal axis emerging through focus
2 striking the centre of the lens passes straight through (if lens is thin)
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F = Focal point
object
Images in Convex lens
vuf
111
vu
f
Image
Real, inverted & diminished
Image formed in convex lens when the object is placed
outside twice the focal length
FF
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Image formed in convex lens when the object is placed at
twice focal length
F = Focal point
object
ImageReal, inverted & same size as object
Images in Convex lens
vuf
111
vu
f
FF
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Image formed in convex lens when the object is placed
between fand 2f
F = Focal point
object
Image
Real, inverted & magnified
Images in Convex lens
vuf
111
vu
f
FF
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Image formed in convex lens when the object is placed at
the focus
F = Focal point
object
Imageat Infinity
Images in Convex lens
vuf
111
u
f
FF
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Image formed in convex lens when the object is placed
inside the Focus
F = Focal point
object
Images in Convex lens
vuf
111
u
f
ImageVirtual, magnified & upright
FF
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rayboxlens
u v
Experiment to find the focal length of a convex lens
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F = Focal point
1. A ray which strikes the lens
travelling parallel to principal
axis is refracted as if it came
from focus
2. A ray striking the
centre of the lens
passes straight
through (if lens is thin)
3. A ray heading for
the focus on striking
the lens is refracted
parallel to principalaxis
To locate the position of an image in
a concave lens we use twoof thefollowing rays of light
Convave lens
FF
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Image formed in concave lens when the object is placed
in front of lens
F = Focal point
object
Images in Concave lens
vuf
111
ImageVirtual, upright &
diminished
v
u
f
FF
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Cornea
IrisPupil
Lens
Optic nerve
Retina
Suspensory
ligament
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Accommodation is the ability of the lens in the eye tochange its focal length so that light from close up and
distant objects always fall on the retina
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light from
distant object
falls short of
retina
light fromdistant object
falls on
retina
with help of a
diverging(concave) lens
Short-sight defect
Corrected
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light from
near object
falls behind
retina
Long-sight defect
Corrected
with help of a
converging (convex)lens
falls on
retinalight fromnear object