Physics 123

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Physics 123
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23. Light Geometric Optics
23.1 The Ray Model of Light 23.2 Reflection -
Plane Mirror 23.3 Spherical Mirrors 23.5
Refraction - Snells law 23.7 Converging and
Diverging Lenses
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Reflection
Angle of incidence equals the angle of reflection
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Image in a Plane Mirror
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Image in a Plane Mirror
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Image in a Plane Mirror
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Image in a Plane Mirror
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Image in a Plane Mirror
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Image in a Plane Mirror
do di
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Spherical Mirrors
Concave mirror
Convex mirror
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Concave Mirror
r f
focus f
radius r
f r /2
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Concave Mirror
A parallel ray reflects through the focus
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Concave Mirror
Solar Cooker!
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Concave Mirror
A ray through the focus reflects parallel
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Concave Mirror
Image is inverted, real, reduced
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Concave Mirror Equation
1 / d o 1 / d i 1 / f
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Concave Mirror Problem
A 3 cm high candle is located 5 cm from a concave
mirror whose radius of curvature is 20 cm. What
are the characteristics of the image?
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Concave Mirror Problem
f 10 cm 1/do 1/ di 1/f 1/5 1/ di
1/10 1/ di - 1/10 di - 10 cm The image is 10
cm behind the mirror, virtual, upright, and
magnified 2X m - di / do
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Concave Mirror Problem
Makeup mirror! If the object is within the focus
of the concave mirror the image is enlarged
(magnified), upright but virtual its all in
your head!!!
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Convex Mirror
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Convex Mirror
Image will ALWAYS be reduced, virtual, upright
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Jurassic Park!
Rear View Mirror Objects in the mirror are closer
than they appear!
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Convex Mirror Equation
1 / d o 1 / d i 1 / f Note f is negative d
i is negative
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Convex Mirror Problem
A 3 cm high candle is located 5 cm from a convex
mirror whose radius of curvature is 20 cm. What
are the characteristics of the image?
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Convex Mirror Problem
f - 10 cm 1/do 1/ di 1/f 1/5 1/ di -
1/10 1/ di - 3/10 di - 3.3 cm The image is
3.3 cm behind the mirror, virtual, upright, and
reduced in size m - di / do m 1 / 3
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Refraction
?i
?r
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Index of Refraction
n sin ?i / sin ?r
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Refraction Problem
The index of refraction of glass is 1.5. A ray
of light is incident on a glass pane at an angle
of 600. Calculate the angle of refraction.
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Refraction Problem
n sin ?i / sin ?r 1.5 sin 600 / sin ?r 1.5
0.866 / sin ?r sin ?r 0.866 / 1.5 sin ?r
0.58 ?r 350
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Converging (convex) Lens
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Converging Lens
When the object is outside the focus, the image
is real and inverted
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Converging Lens
When the object is inside the focus, the image is
virtual, upright, and enlarged.
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Diverging (concave) Lens
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Diverging (concave) Lens
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Diverging (concave) Lens
The image is ALWAYS reduced, upright, virtual
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Lens Problem
A 35 mm slide projector uses a converging lens
with f 20 cm. The screen is 3 m away. How far
is the slide from the lens?
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Lens Problem
1/do 1/ di 1/f 1/do 1/ 300 1/20 1/do
1/20 - 1/ 300 do 21. 4 cm m - di / do m -
300 / 21.4 m -14 Image is real, inverted,
magnified
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Thats all folks!