Can light bounce? Yes! We call this a reflection. Humans have been looking at reflections for...
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- Can light bounce? Yes! We call this a reflection. Humans have
been looking at reflections for thousands of years, however theyre
not always clear.
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- Reflections Why is the reflection blurred? How could you get a
clear reflection?
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- 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.
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- The Law of Reflection Consider what happens when I bounce pass
a basketball. How can I change the angle of the bounce pass?
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- 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.
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- The Law of Reflection
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- Bellringer
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- Updates Sound Quiz SLC today First Regents Review HW due
tomorrow 1-50 MC
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- Objectives
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- The Law of Reflection Smooth vs rough surfaces Which will be a
better reflector? Laser demo
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- 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.
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- Specular Reflection
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- Diffuse Reflection
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- 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?
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- 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.
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- Changing Reflection Types How could you make a diffuse surface
a specular surface? Polish it, or coat it with something to smooth
it over.
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- Flipped Images Why is the reflected image of this pond upside
down?
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- 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?
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- Law of Reflection Tree Solution
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- Practice Problems - 467 Page 467 numbers 1-6 8 minutes
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- 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
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- Bellringer
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- Updates Sound Quiz SLC today First Regents Review HW due
tomorrow 1-50 MC
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- 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?
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- Thirsty?? What is wrong with this pencil?? Have you ever looked
into a pool and it seemed shallower than it was?
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- 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.
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- Refraction The incident angle in all three cases is the same.
What is different? The medium, and the angle of refraction.
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- Refraction
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- 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
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- 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.
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- Snells Law of Refraction
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- 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.
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- 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?
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- Bellringer
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- Updates Missing sound quiz Physics club on Tuesday New SLC
roster Review HW due Friday
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- Snells Law
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- Example
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- 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
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- 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!
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- 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.
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- What is the speed of light?
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- The Index of Refraction
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- Checkpoint
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- 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.
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- Critical Angle
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- Total Internal Reflection
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- 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.
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- Fiber Optics
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- 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.
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- Mirages
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- 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?
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- Index of Refraction Lab Take a moment to read the
procedure.
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- Bellringer
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- Updates Physics Club today New SLC Roster HW due Friday Next
Quiz?
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- Sound Quiz Mod 2: 83 Mod 8: 81
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- 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.
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- Sample Long Answer Problem
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- 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.
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- Bellringer 2 mins to hand in DO WORK STOP
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- Bellringer 2 mins to hand in What is the difference between a
reflected wave and a refracted wave? DO WORK STOP
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- Objectives Be able to answer all questions about reflection and
refraction of light Begin your journey through space and
astronomy.
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- Lyrid Meteor Shower Tonight is the peak of the shower. Look
northeast?
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- Index of Refraction Labs Please hand in your completed index of
refraction labs.
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- 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.
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- 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.
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- Bellringer
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- Updates New SLC Roster HW due Friday Next Quiz?
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- Index of Refraction Lab Calculations and Conclusion
Questions
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- 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!
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- 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.
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- Refraction Bend
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- 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.
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- 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
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- 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
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- 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?
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- 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.
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- Find the angles of refraction Corn Oil Diamond Water Crown
Glass Air
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- Mathematical Proof
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- The Missing Piece
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- Back to the Proof
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- Practice answer in nm
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- Refraction MC
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- Total Internal Reflection Demos What is Total Internal
Reflection? Water Tank
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- Bellringer What is the difference between a reflected wave and
a refracted wave? DO WORK STOP
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- Objectives Be able to answer all questions about reflection and
refraction of light Begin your journey through space and
astronomy.
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- 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.
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- Lenses Lenses use refraction to bend light rays. The way they
are curved changes the amount that they can bend the light
rays.
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- Convex Lens Why does this type of lens focus light beams? The
curved shape changes the incident and refracted angles.
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- Concave Lens Why does this type of lens disperse light beams?
The curved shape change the incident and refracted angles.
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- Computer Demo https://phet.colorado.edu/en/simulation/bending-
light https://phet.colorado.edu/en/simulation/bending- light
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- 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.