Physics 2054C

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Physics 2054C

• Chapter 23 Light

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Wednesdays Quiz

• Reflection (incident angle reflected angle)
• Refraction
• Snells Law.
• Total Internal reflection.
• Lenses
• Lens equation (converging or diverging lens).
• Ray diagrams (converging or diverging).
• Magnification.
• Image classification.

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Reflected Light
The angle of incidence equals the angle of
reflection.
?in
?out
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Refracted Light
The direction changes when the light moves from
material to another. The change depends on the
material. Snells Law determines the
angles N1 sin ?1 N2 sin ?2 The index of
refraction, N, is the ratio of the speed of light
in vacuum to the speed of light in the
material. N c/v c speed of light in
vacuum. v speed of light in material.
glass
air
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Total Internal Reflection
Nair 1, Nwater 1.3
air
(Nw/Na)sin ?w sin ?a
?a
water
?w
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Lenses
1 Parallel Ray 2 Central Ray 3 Focal Ray
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Different Lens Types
Diverging Lens F lt 0 Converging Lens F gt 0
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Lens Equation
1 1 1 F
O I
F
O
I
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Lens Equation Example
1 1 1 F
O I
F 20 cm, O 50 cm
F
O
I
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Lens Equation Example
F 20 cm, O 50 cm
1 1 1 F
O I 1/20 1/50 1/I ? 1/I 1/20
1/50 5/100 2/100 1/I 3/100 ? I 33.3 cm
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Lens Magnification Example
F 20 cm, O 50 cm, I 33.3 cm
Magnification m -I/O m -I/O - 33.3 cm/50
cm m -2/3

• Real Image
• Inverted

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Lens Magnification Example
F 20 cm, O 50 cm, I 33.3 cm
m -I/O - 33.3 cm/50 cm m -2/3 m
-h(image)/h(object)

• Real Image ( I gt 0 )
• Inverted ( m lt 0 )

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Diverging Lens
1
3
object
image
1 Parallel Ray 2 Central Ray 3 Focal Ray
2
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Diverging Lens
1
3
object
image
F - 20 cm O 50 cm Use the Lens Equation
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Diverging Lens w/ Lens Equation
1 1 1 F
O I
F - 20 cm O 50 cm
1/(-20) 1/50 1/I ? 1/I -1/20
1/50 -5/100 2/100 1/I -7/100 ? I
-100/7 - 14.28 cm m -I/O - (-14.28 cm)/(
50 cm ) 2/7 m gt 0 ? Image is upright. I
lt 0 ? image is virtual.