1. Refraction of Light

2. What is Refraction
Although light travels in straight lines, it bends when it passes from one medium to another
Refraction: the bending of light rays as they pass between two different media

3. Why Does Refraction Occur?
Refraction occurs due to changes in the speed of light in different mediums
Different media slow down light by different amounts
The more that light slows down, the more the light is refracted

4. Refraction in Water Demo: Disappearing Coin
Light rays change direction at the surface of the water
The image of the coin appears to be more shallow than the actual coin

5. Refraction in Water

6. Fermat’s Principle
Light will follow the path that takes the least amount of time
In a single medium, the pathway is always a straight line
When travelling from one medium to another the fastest pathway is not a straight line
Which path from A to B
is faster?

7. Angle of Refraction
Refracted ray: ray of light that is bent when entering a second medium
Angle of refraction: angle between the normal and refracted ray

8. Angle of Refraction When travelling from a less dense
medium to a more dense medium,
light bends towards the normal
When travelling from a more dense
medium to a less dense medium,
light bends away from the normal

9. Index of Refraction Speed of light in a vacuum: 3.0 x 108 m/s
Speed of light is less than this in any type of matter
Index of refraction is easier system for describing relative speeds
The amount by which a transparent medium decreases the speed of light

10. Index of Refraction
No units: they cancel! or

12. Given: Speed of light in glass = 1
Given: Speed of light in glass = 1.91 x 108 m/s Speed of light in vacuum = 3.00 x 108 m/s
= 3.00 x 108 m/s x 108 m/s
= 1.57
The refractive index is 1.57

13. Given: Refractive index in water = 1.33 Speed of light in a vacuum = 3.00 x 108 m/s
1.33 = 3.00 x 108 m/s v
v = 2.26 x 108 m/s
The speed of light in water is 2.26 x 108 m/s

14. Dispersion
Dispersion: the refraction of white light into separate wavelengths (colours)
The amount of refraction is different for each colour
Different colours of light travel at different speeds so each refracts a different amount
RRR (Red Refracts Rotten)

15. Dispersion

17. Observing & Tracing Refraction Activity
Materials:
Laser level
Plastic block
White board
Marker
Procedure:
Shine the laser on one side of the block. Observe the incident and refracted rays at different angles of incidence
Draw 1 incident ray on one side of the block (IR1)
Shine the incident ray along IR1. Mark the ray that emerges from the other side as refracted ray 2 (RR2)
Connect IR1 with RR2 inside the block with straight lines

18. Observing & Tracing Refraction Activity
Analysis:
Label what you think is refracted ray 1 (RR1) and incident ray 2 (IR2)
Draw a normal on both surfaces of the block
Measure σi1, σR1, σi2, σR2
What do you notice about σi1, σR2? How about σi2, σR1?

19. Homework
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20. Snell’s Law
There is a relationship between the angles of incidence and refraction of the indices of refraction of 2 media (n)
Snell’s Law applies to refraction of light in any situation regardless of the media

21. Snell’s Law Questions
Light passes from air (n = 1.00) into diamond (n = 2.42) with an angle of incidence of 60.0 degrees. What is the angle of refraction?
What is the index of refraction of a material if the angle of incidence in air is 50.0 degrees and the angle of refraction in the material is 40.0 degrees?
A diamond ring is dropped into water. The index of refraction for diamond is If light strikes the diamond at an angle of incidence of 60.0 degrees, what will be the angle of refraction in diamond?