1. Week 4/5- REFRACTION

2. 1 John says,
‘When hunting a fish under water, you should aim your spear directly at the fish.’
Do you agree?
Yes, of course.
No, because the fish is actually located somewhere else. 
No, because size of objects changes when they are put under water.

3. 2 When sunlight falls on the water surface, which of the following occur(s)?
It is reflected back to the air. 
It refracts into the water. 
It is absorbed by water and
turned into heat.

4. Introduction
Refraction is the bending of light
when the light passes from one medium to another.
air
glass

5. Introduction Useful words to describe refraction of light
angle of incidence
incident ray
normal
air
glass
refracted ray
angle of refraction

6. Introduction
From a less dense to a denser medium
e.g. from air to glass
normal
incident ray
air
glass
refracted ray
Light is bent towards the normal.

7. Introduction From a denser to a less dense medium normal incident ray
e.g. from water to air
air
water
normal
incident ray
refracted ray
Light is bent away from the normal.

8. Laws of refraction
The incident ray,
the refracted ray,
and the normal
all lie in the same plane.
incident ray
normal
normal
air
air
glass
glass
refracted ray
refracted ray

9. Q1 A boy shines a torch under…
A boy shines a torch under water as shown.
Which one shows the correct path of the light ray?
A Path X.
B Path Y.
C Path Z.
D All of them.

10. Q4 True or false: When light is…
True or false: When light is incident on a surface along the normal, only refraction occurs; there is no reflection.
(T/F)

11. 1st statement 2nd statement
Q5 Statements:...
1st statement 2nd statement
Light is bent towards the normal when it passes from air to glass.
Glass has a greater refractive index than air.
true?
true?
Yes
Yes

12. 4 Examples of refraction of light
a Bent chopstick
The chopstick appears bent because of refraction

13. 4 Examples of refraction of light
c Flickering objects in hot air
The object you see through the unstable hot air appears blurred and flickering.

14. Q1 True or false: Light slows…
True or false: Light slows down when it enters a material from air.
(T/F)

15. Q3 True or false: If light travel…
True or false: If light travel at the same speed in all materials, refraction would still occur when it passes from air to water.
(T/F)

16. Refraction Light Bends when coming at an angle
Light slows down or speeds up
Wavelength changes
Frequency remains the same

17. Example
Incident Ray
Less Rigid Medium More Rigid Refracted ray bends towards the normal.
Refracted Ray

18. Index of Refraction, n c : the speed of light in a vacuum,
n = c / v
c : the speed of light in a vacuum,
3 x 108  m/sec
v : speed of light in the medium.
n : medium's index of refraction

19. Q2 True or false: The refractive…
True or false: The refractive index cannot be smaller than 1.
(T/F)

20. Indices of Refraction Vacuum 1.00 Air 1.0003 Water 1.33 Ethanol 1.36
Crown glass 1.52
Quartz 1.52
Diamond 2.42

21. Note
The speed of light has a lower speed in a more optically dense medium.

22. Problem
What is the speed of light in quartz?
Answer: 1.97 x m/s

23. Refraction n1- from n2 - into
When a wave slows down it bends closer to the normal. {less to more – toward} n2>n1
When a wave speed up it bends away from the normal. {BLA – Big ―› Little – Away} n2<n1

24. Q5 Sketch a ray diagram for the...
Sketch a ray diagram for the tip of the chopstick to show why the chopstick looks bent when dipped into water.

25. 4 Examples of refraction of light
b Shallower in water O I
real depth
The depth that the object is actually at is called the real depth.

26. Apparent Depth Diverging rays enter your eyes.
You “think” in Straight Lines.
A virtual image appears to come from point y
                  
R – Real Depth
A – Apparent Depth

27. Apparent Depth
If the chest is 20 m below the surface at what depth will the image appear? Assume nsea water = 1.34

28. Homework Watch and learn: https://www.youtube.com/watch?v=hXe7EVv1y0Q
Memorize Electromagnetic spectrum. (Types of waves, frequency and wavelength ranges)
Solve the problem sheets provided in the class.
In case you lost this. You can print here: