Refraction

1
Refraction

• Refraction
• Total Internal Reflection
• Dispersion

2
Reading Question
To prepare for class today I read
1. 0 to 20 2. 20 to 40 3. 40 to 60 4. 60 to
80 5. 80 to 100
3
Reading Question
Outside of class I use the Workbook
1. Never 2. A little 3. Some 4. A lot
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Reading Question
The reading for today covered
1. reflection 2. refraction 3. total internal
reflection 4. dispersion 5. 1 and 2 6. 2, 3, and 4
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Refraction

• Refraction
• On the table you will find a plastic block. Take
  a clean sheet of paper and place the plastic
  block in the center and draw an outline of the
  block. Remove the block and draw a normal to the
  front surface (larger) near the center of the
  face. Label the normal N. Place the plastic
  block back in the outline. Get the light box and
  position the box so that the beam strikes the
  surface at the normal and making an angle of
  about 200 to 300 to the normal. Observe the beam
  inside the plastic block.

6
Refraction

• Observe the beam inside the plastic block. Does
  the beam bend toward the normal or away from the
  normal?

Towards the normal.
light box
N
7
Refraction

• Slowly change the incident angle to 400 to 500
  and observe the transmitted or refracted beam.
  Does it behave the same way as for the smaller
  angle?
• The plastic is said to be denser than air. This
  is an optical density and just means that the
  index of refraction is greater. What is the
  index of refraction for air?
• index of refraction of air _______
• Write a statement that describes the light beam
  as it passes from a less dense to a more dense
  material.

yes
1.0
When passing into a more dense material the
beam bends toward the normal
8
Refraction

• Return the light box so that the beam makes an
  angle of about 500 to the normal and trace a line
  on the paper for the incident beam and the
  refracted beam. Use a protractor and measure the
  angles. Use Snells law to find the index of
  refraction for the plastic block.

9
Refraction
10
Refraction
11
Refraction

• Remove the plastic block and draw a normal to the
  back surface near the center of the face.
  Replace the block and position the beam so that
  the beam hits the front surface, passes through
  the block, and emerges from the back surface at
  the normal to the surface. Now we will study the
  beam as it leaves the block. Does the beam bend
  toward or away from the normal as it emerges from
  the block?

N
12
Refraction

• Write a statement that describes a light beam as
  it passes from a more dense to a less dense
  material.
• Does this agree with Snells law?

When passing from a more dense material into a
less dense material the beam bends away from
the normal
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Student Workbook
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Student Workbook
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Refraction

• Lets look at a typical refraction problem. At
  the front of the room is a fish tank full of
  water with a coin on the bottom. Walk up and
  observe the coin through the top water surface.
  Compare the coin in the water to the coin on the
  table beside the tank. Do they appear to be at
  the same depth or distance below the surface?
  Which coin looks deeper or farther away?

16
Refraction

• Lets see if we can understand this. Below is a
  drawing of the coin and tank. Assume that air
  has an index of refraction of 1.0 and that water
  has an index of refraction of 1.33. In the
  drawing you see a light beam leaving the coin and
  striking the surface at an angle of 500.
• Use Snells law and find the emerging beam.

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Refraction

• Use Snells law and find the emerging beam.
• Use a protractor the draw the refracted beam.

medium 2 air
590
medium 1 water
400
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Refraction

• When your eye sees the refracted beam your brain
  interprets the beam as coming in a straight line.
  Extend the refracted beam back into the water in
  a straight line. Your brain thinks the coin is
  somewhere along this line. To find where we need
  another beam.

medium 2 air
590
medium 1 water
400
19
Refraction

• We will use RAYTRACE. It is much easier.

20
Refraction

• Calculate the percent that the coin appears to be
  to the actual depth of the coin.
• The coin appears to be only _____ per cent as
  deep as it really is.
• Is this depth constant or does it depend on the
  angle you view the coin?

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Student Workbook
22
Refraction

• Another example.

23
Refraction

• Mirage

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Class Question
A light ray travels from medium 1 to medium 3 as
shown. For these media,
1. n3 lt n1. 2. n3 n1. 3. n3 gt n1. 4. We
cant compare n1 to n3 without knowing n2.
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Class Question
A light ray travels from medium 1 to medium 3 as
shown. For these media,
1. n3 lt n1. 2. n3 n1. 3. n3 gt n1. 4. We
cant compare n1 to n3 without knowing n2.
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Refraction

• Total Internal Reflection
• Get the plastic from the box on the table. Place
  the plastic on a clean sheet of paper with the
  triangular shaped end toward you and the larger
  flat side to your right. Trace the shape of the
  object on the paper. Remove the object and draw
  a normal to the flat surface near the center of
  the flat side. Place the plastic back in
  position and position the beam so that the beam
  exits the flat side along the normal. Now slowly
  move the beam to the left about 100 so that the
  beam exits at the normal. Trace the refracted
  beam. Move the beam to 200, 300, and so on until
  the refracted beam is parallel to the flat
  surface. Mark the incident beam when the
  refracted beam is parallel to the surface by
  marking the point where the laser beam strikes
  the plastic and drawing a line from this point to
  where the beam exits the plastic.

27
Refraction

• Measure the incident angle and calculate the
  index of refraction for the plastic.
• incident angle _________
• index of refraction ______

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Refraction

• Total Internal Reflection

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Refraction

• Total Internal Reflection

30
Refraction

• Fiber Optics

31
Refraction

• Total internal Reflection

Fiber optical cable
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Refraction

• Whats going on?

33
Refraction
Dispersion
34
Refraction

• We will use RAYTRACE to study dispersion.

Refractive index, n
Red Green Blue
1.516 1.528 1.537
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Reflection, Refraction, Dispersion
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Refraction
We will use RAYTRACE to show that the maximum
angle is 42 degrees.
37
Refraction
Double rainbow
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(Not due to )Refraction
Why is the sky blue?
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Student Workbook
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Student Workbook
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Student Workbook
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(Not due to )Refraction

• Polarization by Reflection

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Refraction
Rainbow