1. Chapter 11
Refraction

2. THE REFRACTION OF LIGHT
KEY QUESTION: How does light behave as it travels from one medium into another?
Key Concepts
Light changes direction predictably as it travels through different transparent media.
Light bends toward the normal when it slows down in a medium with a higher index of refraction.
Total internal reflection may occur when an incident ray is aimed at a medium with a lower index of refraction.
Many optical devices make use of the refraction and reflection of light.
The refraction and reflection of light can be used to explain natural phenomena.
Understanding the behaviour of light is key to many careers.

3. Learning Goals To better understand what it means for light to refract
To understand the properties of light traveling through various mediums

4. What is Refraction? Light travels in straight lines through air
But what happens when it travels from one material into another?
Remember, there light can travel through different mediums

5. What is Refraction?
You probably noticed the strange phenomenon of a spoon or stir stick, when placed in a glass of water, looking somewhat disconnected at the surface of the water.
The spoon is not really disconnected. It is made of a solid material
So what is happening?
Why does an object appear disconnected, or broken, at the water’s surface?
This is what we will soon be finding out!

6. The Bending of Light
When light is traveling along one path (air), and changes its direction when it goes into another medium (like the water)
The light rays are bent, because of an phenomenon called REFRACTION
Refraction causes interesting effects whenever light travels from one medium to another

7. The Bending of Light

8. What Causes Refraction?
The refraction of light becomes obvious when you shine a powerful beam of light into water at an angle
But, Why does the direction change?

9. What Causes Refraction?
A useful analogy is to think of a wagon travelling at an angle from pavement onto sand
When the right front wheel hits the sand, it slows down
The left front wheel, however, does not slow down because it is still on the pavement
This results in the wagon pivoting about the slower right front wheel
So the direction of the wagon changes as it moves from pavement onto sand.

10. What Causes Refraction?

11. How Fast Is the Speed of Light?
The analogy of refraction using the wagon involves one of the front wheels slowing down as the wagon travels from one surface onto another
The same thing happens with light when moving through different mediums

12. How Fast Is the Speed of Light?
The speed of light in water is different from the speed of light in air
This is WHY LIGHT REFRACTS!!
Where:
Light travels at a speed of 3.00 × 108 m/s
In a vacuum, at a speed of 2.26 × 108 m/s
In water, and at a speed of 1.76 × 108 m/s in acrylic.

13. The Rules for Refraction
Because the speed of light changes depending on the medium through which it is travelling
It is possible to make Three statements about refraction in general and about the angle of refraction in particular

14. The Rules for Refraction
There are three predictable results
when light refracts:
The incident ray, the refracted ray, and the normal all lie in the same plane
Light bends toward the normal if it travels slower in the second medium than in the first
Light bends away from
the normal if it travels
faster in the second
Medium than in the first.
incident ray
refracted ray
angle of incidence
angle of refraction

15. The Rules for Refraction

16. The Rules for Refraction

17. The Rules for Refraction

18. The Bent Spoon
Using the concept of refraction, it is possible to explain why a spoon in a glass of water appears bent

19. The Bent Spoon
Light coming from the part of the spoon below the water’s surface must travel through the water and into air
The speed of light increases as light goes from water into air
So, if it hits the water–air boundary at an angle, light will bend away from the normal

20. The Bent Spoon
The human brain perceives light to travel in a straight line, so it will project these light rays backwards to a virtual light source behind the real spoon
This is just like when the brain projects light rays to form a virtual image in a plane mirror! (yay!)

21. Partial Reflection & Refraction
Reflection + Refraction go Together!
Some of the light that strikes water is reflected off the water, but a large amount of light is also refracted as it enters the water and illuminates the water below the surface

22. Partial Reflection & Refraction

23. Partial Reflection & Refraction
A transparent window exhibits the same property that light can be both reflected and refracted at the same time.
This is called Partial Reflection and Refraction

24. Partial Reflection & Refraction
For example: A glass building has
Light enter into it(Refraction)
And some light reflected off (Reflection)

25. Partial Reflection & Refraction
This effect is enhanced if glass has a special film coating behind it allows some of the incident light to be refracted but that also reflects much of the incident light
This results in a mirrored surface that you can see through, but others cannot.
This type of surface is called a silvered two-way mirror, and it is exactly how mirrored sunglasses work

26. Partial Reflection & Refraction

28. Checking for Understanding

29. Answers FASTER in a medium = AWAY from the normal
SLOWER in a medium = CLOSER to the normal

30. Checking for Understanding