Can light bounce? Yes! We call this a reflection. Humans have
been looking at reflections for thousands of years, however theyre
not always clear.
Slide 4
Reflections Why is the reflection blurred? How could you get a
clear reflection?
Slide 5
The Egyptians Almost 4,000 years ago the Egyptians realized
that only smooth ponds produce clear reflections. However it wasnt
until 1835 when Justus von Liebig, a German scientist, developed a
method of coating glass with silver to produce a sharp,
well-defined, reflected image.
Slide 6
The Law of Reflection Consider what happens when I bounce pass
a basketball. How can I change the angle of the bounce pass?
Slide 7
The Law of Reflection Light reflects the same way the
basketball does. Laser Demo The Law of Reflection: The angle that a
reflected ray makes as measured from the normal to a reflective
surface equals the angle that the incident ray makes as measured
from the same normal.
Slide 8
The Law of Reflection
Slide 9
Bellringer
Slide 10
Updates Sound Quiz SLC today First Regents Review HW due
tomorrow 1-50 MC
Slide 11
Objectives
Slide 12
The Law of Reflection Smooth vs rough surfaces Which will be a
better reflector? Laser demo
Slide 13
The Law of Reflection Specular Reflection is when parallel
light rays are reflected in parallel Diffuse Reflection is when
parallel light rays are not reflected in parallel but instead they
are scattered. This is what allows us to read text or see images
from various angles.
Slide 14
Specular Reflection
Slide 15
Diffuse Reflection
Slide 16
Checkpoint 1. What is the law of reflection? 2. What is the
difference between specular and diffuse reflection? 1. Which one is
used by mirrors?
Slide 17
The Law of Reflection The law of reflection still applies to
both types of reflection. No matter how much light reflects off a
wall or a sheet of paper, you will never be able to use them as
mirrors. The light that reflects off the wall or paper is how we
see the wall or paper.
Slide 18
Changing Reflection Types How could you make a diffuse surface
a specular surface? Polish it, or coat it with something to smooth
it over.
Slide 19
Flipped Images Why is the reflected image of this pond upside
down?
Slide 20
Law of Reflection What is the angle of incidence of the highest
leaf if the tree is 10 meters tall and its reflection is 20 meters
long? If the observer is 1.83 meters tall, how far away from the
base of the tree are they?
Slide 21
Law of Reflection Tree Solution
Slide 22
Practice Problems - 467 Page 467 numbers 1-6 8 minutes
Slide 23
Practice Problem Answers 1. Water fills in the rough areas and
makes the surface smoother. The surface normals are then parallel.
2. 35 3. 42, 48, 84 4. 51 5. 30 6. 90
Slide 24
Bellringer
Slide 25
Updates Sound Quiz SLC today First Regents Review HW due
tomorrow 1-50 MC
Slide 26
Light and Boundaries What happens when light encounters a
boundary like a window? Some light is transmitted through the
window and some light is reflected back. Laser out the window demo
Is this a property of a wave or a particle?
Slide 27
Thirsty?? What is wrong with this pencil?? Have you ever looked
into a pool and it seemed shallower than it was?
Slide 28
Refraction These phenomena happen because the light rays bend
as they enter a new medium. Refraction: The change in direction of
waves at the boundary between two different mediums.
Slide 29
Refraction The incident angle in all three cases is the same.
What is different? The medium, and the angle of refraction.
Slide 30
Refraction
Slide 31
Willebrord Snell Snell came up with a mathematical law to
relate the angle of incidence with the angle of refraction. He did
this using a light source and a piece of glass. He shot the light
at various angles and measured the results. Then he plotted his
data and found a mathematical relationship that fit and could
correctly predict the outcome. Lets try it! Watch your eyeslaser
beam
Slide 32
Snells Findings He found that the sines of the angles were
related! Woo trig! He also found that each material had its own
index of refraction (n) which determines the angle of refraction of
light as it crosses the boundary between two mediums.
Slide 33
Snells Law of Refraction
Slide 34
Index of Refraction By doing experiments with other
combinations of mediums Snell found the index of refraction of many
different materials. A table of the different indices of refraction
can be found in the reference table.
Slide 35
Beaker Demo Will light bend as it goes from air to corn oil?
Why? Will light bend as it goes from corn oil to corn oil? Why?
Will light bend as it goes from corn oil to another medium that has
the same n as corn oil? Why? Can we make something invisible?
Slide 36
Bellringer
Slide 37
Updates Missing sound quiz Physics club on Tuesday New SLC
roster Review HW due Friday
Slide 38
Snells Law
Slide 39
Example
Slide 40
Practice Complete practice problems 1-5 on page 494 of the
textbook. Answers 1. 26.3 degrees 2. 34.2 degrees 3. 17.0 degrees
4. 1.5 5. The medium is float glass
Slide 41
Where does n come from? The index of refraction (n) describes
how much light bends as it enters a medium, but why does it bend?
The light bends because it is changing its speed!
Slide 42
The speed of light The speed of light can never be faster than
when it is traveling through a vacuum, but it can be slower when
traveling through a different medium. The index of refraction is
the ratio of the speed of light in a vacuum to the speed of light
in the medium.
Slide 43
What is the speed of light?
Slide 44
The Index of Refraction
Slide 45
Checkpoint
Slide 46
Critical Angle As the light travels from a medium of higher n
to lower n, the angle of refraction is larger than the angle of
incidence. Critical Angle: A certain angle of incidence where the
refracted light ray lies along the boundary of the two
mediums.
Slide 47
Critical Angle
Slide 48
Total Internal Reflection
Slide 49
If youre under water in a pool and looking up at the surface
you may not be able to see whats above the surface. Fiber optic
cables use this phenomena to transmit data very efficiently and at
the speed of light.
Slide 50
Fiber Optics
Slide 51
Slide 52
Mirages As the ground heats up from the sun it creates a thin
layer of much warmer air near the ground. This layer of hot air has
a smaller n value than the air at eye level. This difference in n
makes the light rays of the sky and usually an object reflect of
the cool and hot air boundary.
Slide 53
Mirages
Slide 54
Checkpoint 1. What conditions are necessary for total internal
reflection to occur? 2. What are two examples of total internal
reflection in real life? 3. What causes mirages?
Slide 55
Index of Refraction Lab Take a moment to read the
procedure.
Slide 56
Bellringer
Slide 57
Updates Physics Club today New SLC Roster HW due Friday Next
Quiz?
Slide 58
Sound Quiz Mod 2: 83 Mod 8: 81
Slide 59
Index of Refraction Lab How many calculations must you show?
Once youve calculated your three different average experimental n
values come ask me for the theoretical n values.
Slide 60
Sample Long Answer Problem
Slide 61
Index of Refraction Lab How many calculations must you show?
Once youve calculated your three different average experimental n
values come ask me for the theoretical n values.
Slide 62
Bellringer 2 mins to hand in DO WORK STOP
Slide 63
Bellringer 2 mins to hand in What is the difference between a
reflected wave and a refracted wave? DO WORK STOP
Slide 64
Objectives Be able to answer all questions about reflection and
refraction of light Begin your journey through space and
astronomy.
Slide 65
Lyrid Meteor Shower Tonight is the peak of the shower. Look
northeast?
Slide 66
Index of Refraction Labs Please hand in your completed index of
refraction labs.
Slide 67
Lab Checklist - Missing All labs (except Series-Parallel
Circuits) are out of 50 points. You need a grade of 33 or higher
for the lab to count towards your lab minutes. Check off the labs
you have in your folder and calculate your total number of lab
minutes. If you have someones lab give it to them or me. When youre
done bring me you lab folder and checklist.
Slide 68
Homework Complete all the multiple choice questions. We will
spend one mod on Friday reviewing it. Id rather you not do it at
all than cheat. The Regents exam is less than two months away. If
anyone fails I will delete you from my memory. If you do really
well you may be sent to the Physics Hall of Fame.
Slide 69
Bellringer
Slide 70
Updates New SLC Roster HW due Friday Next Quiz?
Slide 71
Index of Refraction Lab Calculations and Conclusion
Questions
Slide 72
Physics Hall of Fame If you have one of the three highest
scores on the Regents exam your name will be placed on the Physics
Hall of Fame plaque!
Slide 73
Refraction Bend If light goes from a lower n to a higher n
(slows down) it will bend towards the normal line. If light goes
from a higher n to a lower n (speeds up) it will bend away from the
normal line.
Slide 74
Refraction Bend
Slide 75
Refraction Bend Practice Which n value is greater? n2 because
the refracted light is bending towards the normal. Which medium is
the light traveling through faster? The top one because it has a
lower n value.
Slide 76
Refraction Practice Complete questions 37 to 40 on page 514 in
the next 8 minutes! 37. The angle of incidence is larger than the
angle of refraction b/c air has a smaller index of refraction 38.
The angle of incidence is smaller than the angle of refraction b/c
glass has a larger index of refraction
Slide 77
Refraction Practice 39. The term critical angle refers to the
incident angle that causes the refracted ray to lie right along the
boundary of the substance when a ray is passing from a region of
higher index of refraction to a region of lower index of
refraction. If the incident angle exceeds the critical angle, total
internal reflection will occur. 40. C>D>B>A
Slide 78
Pyro Board Oh what you can make once you know physics!
https://www.youtube.com/watch?v=2awbKQ2DLRE What is a standing
wave? What is an antinode? What determines what frequencies will
stand in a pipe?
Slide 79
RR Test MC Review Law of Reflection Two types of reflective
surfaces Snells Law Calculate n values using velocity and c Ratios
of index of refraction, velocity, and wavelength of light at
boundaries.
Slide 80
Find the angles of refraction Corn Oil Diamond Water Crown
Glass Air
Slide 81
Slide 82
Mathematical Proof
Slide 83
The Missing Piece
Slide 84
Back to the Proof
Slide 85
Practice answer in nm
Slide 86
Slide 87
Refraction MC
Slide 88
Total Internal Reflection Demos What is Total Internal
Reflection? Water Tank
Slide 89
Bellringer What is the difference between a reflected wave and
a refracted wave? DO WORK STOP
Slide 90
Objectives Be able to answer all questions about reflection and
refraction of light Begin your journey through space and
astronomy.
Slide 91
Lenses Two types of lenses 1. Convex A lens that is thicker at
the center than at the edges. 2. Concave A lens that is thinner at
the center than at the edges.
Slide 92
Lenses Lenses use refraction to bend light rays. The way they
are curved changes the amount that they can bend the light
rays.
Slide 93
Convex Lens Why does this type of lens focus light beams? The
curved shape changes the incident and refracted angles.
Slide 94
Concave Lens Why does this type of lens disperse light beams?
The curved shape change the incident and refracted angles.
RR Test Law of Reflection Two types of reflective surfaces
Snells Law Calculate n values using velocity and c Ratios of index
of refraction, velocity, and wavelength of light at
boundaries.