18_LectureOutlines
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Transcript 18_LectureOutlines
Chapter 18
Ray Optics
Topics:
• The ray model of light
• Reflection
• Refraction
• Dispersion
• Ray tracing for lenses
• Ray tracing for mirrors
Sample question:
Why are there two images of this turtle in an aquarium, and why
does each image appear to be a different size?
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Slide 18-1
Reading Quiz
1. When an object like a tree is illuminated by the sun, and you
are looking toward the tree, light rays leave the object
A. only from points at the top and base of the tree, but in
every direction.
B. from every point on the surface of the tree, but only toward
your eyes.
C. only from points at the top and base of the tree, but only
toward your eyes
D. from every point on the surface of the tree and in every
direction.
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Slide 18-2
Answer
1. When an object like a tree is illuminated by the sun, and you
are looking toward the tree, light rays leave the object
D. from every point on the surface of the tree and in every
direction.
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Slide 18-3
Reading Quiz
2. A light ray can change direction when going from one material
into another. This phenomenon is known as
A. reflection.
B. absorption.
C. refraction.
D. scattering.
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Slide 18-4
Answer
2. A light ray can change direction when going from one material
into another. This phenomenon is known as
C. refraction.
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Slide 18-5
The Ray Model of Light
Light rays travel in straight lines.
Light rays can cross.
An object is a source of light rays.
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A light ray travels forever unless it
interacts with matter.
The eye sees by focusing a bundle of rays.
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Sources of Light Rays: Self-Luminous Objects
A ray source
A point source
An extended source
A parallel-ray source
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Slide 18-7
Seeing Objects
Seeing a point or extended source
Seeing an object
by scattered light
Seeing a ray source
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Slide 18-8
Shadows
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Slide 18-9
Example
If the aperture is very small, how far apart on the screen built into
the left side of the box are the images of the point-like red and
green light sources?
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Slide 18-10
Example
If the aperture is a circle 1 cm in diameter, what are the size and
shape of the image of the green point-like light source? Do you
need to know how far below the center of the aperture that source
is?
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Slide 18-11
The Law of Reflection
1.The incident ray and the
reflected ray are in the same
plane normal to the surface,
and
2.The angle of reflection
equals the angle of incidence:
θ r = θi .
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Slide 18-12
The Plane Mirror
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Slide 18-13
Refraction
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Slide 18-14
Snell’s Law of Refraction
n1 sin1 n2 sin2
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Slide 18-15
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Slide 18-16
Example
What is the index of refraction of the plastic if a ray is refracted as in
the figure?
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Slide 18-17
Total Internal Reflection
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Slide 18-18
Color and Dispersion
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Slide 18-19
Thin Lenses and Ray Tracing
The focal point of a
converging lens
The focal point of a
diverging lens
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Slide 18-20
Three Important Sets of Rays: Converging Lenses
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Slide 18-21
Ray Tracing: Real Images
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Slide 18-22
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Slide 18-23
Checking Understanding
Which of these ray diagrams is possibly correct?
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Slide 18-24
Answer
Which of these ray diagrams is possibly correct?
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Slide 18-25
Magnification
h s
m
h
s
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Slide 18-26
Ray Tracing: Virtual Images
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Three Important Sets of Rays: Converging Lenses
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Slide 18-28
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Slide 18-29
Checking Understanding
In this figure the image is produced by a lens. At
which position A–E is the lens?
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Slide 18-30
Answer
In this figure the image is produced by a lens. At
which position A–E is the lens?
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Slide 18-31
Spherical Mirrors and Ray Tracing
The focal point of a
concave mirror
The focal point of a
convex mirror
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Slide 18-32
Three Sets of Special Rays for a Concave Mirror
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Slide 18-33
A Real Image Formed by a Concave Mirror
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Slide 18-34
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Three Sets of Special Rays for a Convex Mirror
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Slide 18-36
Ray Tracing for a Convex Mirror
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Slide 18-37
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Slide 18-38