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# Refraction PowerPoint PPT Presentation

Refraction. Refraction Total Internal Reflection Dispersion. 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%. Reading Question. Outside of class I use the Workbook. 1. Never 2. A little 3. Some 4. A lot.

Refraction

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## Refraction

Refraction

Total Internal Reflection

Dispersion

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%

Outside of class I use the Workbook

1. Never

2. A little

3. Some

4. A lot

1. reflection

2. refraction

3. total internal reflection

4. dispersion

5. 1 and 2

6. 2, 3, and 4

### 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.

### Refraction

Towards the normal.

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

light box

N

### 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

### 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 Snell’s law to find the index of refraction for the plastic block.

### 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

Yes. When n2 is smaller than n1, then sin q2 has to be larger than sinq1.

### 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 Snell’s law?

When passing from a “more dense” material into a “less dense” material the beam bends away from the normal

### Refraction

• Let’s 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?

0

50

### Refraction

• Let’s 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 Snell’s law and find the emerging beam.

0

50

### Refraction

• Use Snell’s law and find the emerging beam.

• Use a protractor the draw the refracted beam.

medium 2 air

590

medium 1 water

400

0

50

### 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

### Refraction

• We will use RAYTRACE. It is much easier.

### 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?

### Refraction

• Another example.

• Mirage

### Class Question

A light ray travels from medium 1 to medium 3 as shown. For these media,

1. n3 < n1.

2. n3 = n1.

3. n3 > n1.

4. We can’t compare n1 to n3 without knowing n2.

### Class Question

A light ray travels from medium 1 to medium 3 as shown. For these media,

1. n3 < n1.

2. n3 = n1.

3. n3 > n1.

4. We can’t compare n1 to n3 without knowing n2.

### 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.

### Refraction

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

incident angle _________

index of refraction ______

### Refraction

• Total Internal Reflection

### Refraction

• Total Internal Reflection

• Fiber Optics

### Refraction

• Total internal Reflection

Fiber optical cable

### Refraction

• What’s going on?

Dispersion

### Refraction

• We will use RAYTRACE to study dispersion.

Refractive index, n

Red

Green

Blue

1.516

1.528

1.537

### Refraction

We will use RAYTRACE to show that the maximum angle is 42 degrees.

Refraction

Double rainbow

(Not due to )Refraction

Why is the sky blue?

### (Not due to )Refraction

• Polarization by Reflection

Refraction

Rainbow