Chapter 29
Reflection & Refraction
May 27 – 30
Mr. Gaydos
Chapter 29 Notes
I. Introduction:
A. Reflection: Waves incident upon a surface,
some or all of the energy bounces back.
B. Refraction: Waves incident upon a medium,
waves are bent as they enter & travel within
the medium.
Chapter 29 Outline
• Reflection Video
• https://www.youtube.com/watch?v=RlSSy8K_
Gos&list=PL5C55F4122B03492C
Chapter 29 Notes
II. Reflection (Section 29.1)
A. When waves strike a boundary surface between two
mediums, some or all of the energy bounces back.
They Reflect off of the Boundary.
B. The amount of energy reflected back vs. the
amount of energy transmitted depends on the
composition of each medium.
C. Total Reflection: Boundary between Medium 1 & 2
very rigid; Medium #2 >> dense than Medium #1
D. Partial Reflection: Boundary between
Medium 1 & 2 not very rigid; Medium #2 = or <
dense than Medium #1
Chapter 29 Notes
III. Law of Reflection (Section 29.2)
A. The Law:
Angle of Incidence (Ѳi) = Angle of Reflection (Ѳr)
B. What does this mean?
A wave leaves a reflecting boundary at the same angle it
arrives
C. Boundary Conditions
1. Rigid or Flexible?
1. Smooth or Rough?
D. Ray Diagrams
E. Chapter 29 Problem Set #1
Chapter 29 Notes
• IV. Mirrors: Three Types (Section 29.3)
A. Plane (Flat) Mirror
1. Reflecting surface is Flat
2. Line of Sight (LoS)
3. Image Position (Relative to object’s location)
4. Image Size
5. Image’s Orientation
Chapter 29 Notes
IV. Mirrors: Three Types (Section 29.3)
B. Concave Mirror
1. Reflecting surface is Bowed away from object
2. Line of Sight (LoS)
3. Image Position (Relative to object’s location)
4. Image Size
5. Image’s Orientation
Chapter 29 Notes
IV. Mirrors: Three Types (Section 29.3)
C. Convex Mirror
1. Reflecting surface is Bowed towards from object
2. Line of Sight (LoS)
3. Image Position (Relative to object’s location)
4. Image Size
5. Image’s Orientation
Chapter 29 Notes
V. Diffuse Reflection (Section 29.4)
A. Light Reflected off of a “Rough” surface.
B. Light is reflected in many directions.
C. Can see light easily from Rough surface but
need to be at correct angle to see reflected light
from a mirror.
D. Law of Reflection still holds but so many
Boundaries, Normals, Angles of Incidence (Ѳi),
Angles of Reflection (Ѳr) on rough surface that
it may appear that the Law doesn’t hold but it
does at the microscopic level
Chapter 29 Notes
VI. Reflection of Sound (Section 29.5)
A. Sound Waves are reflected and are
subject to the same Law of Reflection as
is Light.
B. Multiple reflections of sound are called
reverberations.
Chapter 29 Notes
VII. Refraction (Section 29.6)
A. The bending of a wave front when one
side of the wave moves slower than the
rest of the wave.
B. As a wave front encounters a boundary,
it will bend in towards the extension of
the Normal OR outwards away from
the Normal depending on the density
of the two mediums separated by the
boundary.
C. Rays can be drawn perpendicular to the
wave fronts to model wave movement &
refraction.
Chapter 29 Notes
VIII. Refraction of Sound (Section 29.7)
A. Sound waves are bent due to uneven
temperatures that exist in the medium
in which sound waves travel.
B. Sound travels faster in warm air.
C. Sound can be heard at night better than
during the day? Yes because the sound
waves are bent down toward the
ground which allows them to travel farther
Chapter 29 Notes
IX. Refraction of Light (Section 29.8)
A. Light waves bend when traveling from one
medium to another
B. Index of Refraction:
1. The mathematical relationship that defines
the speed of light in a vacuum vs. its speed
in a medium.
2. n = speed of light in a vacuum/speed of light
in a material
n = LSvac/LSmed
C. Snell’s Law:
n sin Ѳ = n’ sin Ѳ’
Chapter 29 Notes
X. Atmospheric Refraction (Section 29.9)
A. Speed of Light only 0.03% less than in a
vacuum.
B. On Hot days Refraction can be
noticeable, Mirages may form,
especially on hot streets.
C. Even though the sun has set, observer
can still see it. Why?
Chapter 29 Notes
XI. Dispersion in a Prism
A. Light slows down when traveling in a medium.
B. The degree of “speed reduction” depends
on the medium and the frequency of light.
C. Since different frequencies of light travel
at different speeds in a medium, they will
be bent at different angles.
D. This difference in angle results in the
colors in white light being separated.
E. This process is called dispersion
F. The color violet is bent the most,
red is bent the least.
Chapter 29 Notes
XII. The Rainbow:
A. Dispersion on an atmospheric scale.
B. Water Droplets in the atmosphere act
as a multitude of tiny prisms.
C. If viewed from an aircraft high enough
the rain “bow” would be a complete
circle. We see a bow because the
ground gets in the way.
Chapter 29 Notes
XIII. Total Internal Reflection (Section 29.12)
A. Condition when light rays cannot exit a
medium but are only reflected within
the medium.
B. Critical Angle:
a. The angle at which a beam of light
no longer emerges from a given
medium.
b. For water/air interface, the critical
angle from the normal is 48 °.
Chapter 29 Notes
• XIII. Total Internal Reflection (Section 29.12)
C. Diamonds
1. Smallest Critical Angle
2. Small angle results in most light entering a
diamond being totally internally reflected.
3. Light entering through one facet (face) is
internally reflected many times before exiting
through another facet.
D. Optical Fibers:
1. Light Pipes
2. Employs total internal reflection to carry light
along discrete, dedicated paths much like
metallic wires but without the weight, loss
and cost.
Discovery
Key Terms
A. Line of Sight: The straight line along which a light
ray passes from an object to our eyes allowing
us to see the object.
B. Reflection: The bouncing of light off of a Boundary
Surface.
C. Law of Reflection (Ray Diagram)
1. Angle of Incidence (Ѳi) = Angle of Reflection (Ѳr)
(in Degrees or Radians)
2. Normal to Reflecting Boundary: A line at 90 degrees
to the Boundary Surface
3. Angle of Incidence (Ѳi): The angle an incident light ray
makes with the Normal to the boundary surface
4. Angle of Reflection (Ѳr): The angle a reflective light ray
makes with the Normal to the boundary surface
Discovery
D. Mirror: A Reflecting Boundary
1. Plane (Flat): A mirror whose reflecting
surface is flat.
2. Concave: A mirror whose reflecting surface
is curved away from the object.
3. Convex: A mirror whose reflecting surface
is curved towards the object.
E. Light Pollution: The uncontrolled spread of light
where it is not beneficial or desired.
F. Noise Pollution: The uncontrolled spread of noise
where it is not beneficial or desired.
Discovery
G. Critical Angle: The minimum angle of
incidence for which a light ray is totally
reflected within a medium.
H. Dispersion: The separation of light into
colors arranged according to their frequency,
by interaction with a prism or diffraction
grating.
I. Mirage: A floating image that appears in the
distance and is due to the refraction of light
in the earth’s atmosphere.
J. Echo: Reflected Sound
K. Reverberation: The persistence of sound,
as in an echo, due to multiple reflections.
Discovery
L. Total Internal Reflection: The 100% reflection
(with no transmission) of light that strikes the
boundary between two media at an angle greater
than the critical angle.
M. Virtual Image: An image formed through reflection
or refraction that can be seen by an observer but
cannot be projected on a screen because light from
the object does not actually come to a focus.
N. Wave Front: The crest, trough, or any continuous
portion of a two dimensional or three dimensional
wave in which the vibrations are all the same way
at the same time.
O. Field of View: The maximum area that an image can
be viewed in a mirror by an observer.
Discovery
P. Refraction: The bending of a wave front
when one side of the wave
moves slower than the
rest of the wave.
Q. Diffuse Reflection: The reflection of light
rays from a rough surface that
results in the light rays being
reflected in many directions.
R. Optical Fiber: A light Pipe that transports light
along a fixed path much like a length of
wire.