1. Unit 9:
Light and Optics

2. The Electromagnetic Spectrum
German Physicist Willhelm Rontgen’s wife’s finger (1895) (radiation dose 1,500 times greater than today’s dosage) (video)
Food Irradiation – (Article)
(Video)
Night Vision
(Video)

3. Why can Blu-Ray discs hold more data?
The Electromagnetic Spectrum
Why can Blu-Ray discs hold more data?
Min. Capacity
0.7 GB
4.7 GB
15 GB
25 GB

4. I. Electromagnetic (EM) Waves
_______________charges create __________ and ___________ fields
ACCELERATING
ELECTRIC
MAGNETIC
These fields create __________________________
ELECTROMAGNETIC WAVES
Electric field
Magnetic field
Notes:
Electric field is perpendicular to magnetic field
Both fields are perpendicular to the direction of energy flow 4

5. I. Electromagnetic (EM) Waves
Characteristics of EM Waves
1. EM waves are ______________ waves. (where the disturbance is ________________ to motion of energy.
TRANSVERSE
PERPENDICULAR
VACUUM
EM waves can travel through a __________ or a ________________
CELL PHONE VACUUM PUMP DEMO
MATERIAL SUBSTANCE
3. All EM waves travel at the speed of ________ ( ) in a ____________
LIGHT c
VACUUM 5

6. I. Electromagnetic (EM) Waves
Equation (See Ref. Tabs.)
f = frequency
v = λ f
λ = wavelength
v = c = speed of light (3.00 x 10 8 m/s)
(or 670,616,629 mph or 186,282 miles/s)
It takes 8 minutes 17 seconds for light from the sun to reach us (91 million miles) 6

7. II. The Electromagnetic Spectrum
EM energy (wave) is categorized by its wavelength and frequency.
Visible light makes up only about _______ of the electromagnetic spectrum.
1 % 7

8. II. The Electromagnetic Spectrum
Example: What is the wavelength of an E-M a wave traveling in a vacuum that has a frequency of 4.13x1013 Hz? How is this energy classified on the electromagnetic spectrum? 8

9. III. Proof Light is a Wave
A. Polarization:
Visual light consists of a bunch of EM waves oscillating in random directions
(Un-polarized Light)
Linear Polarized light is when EM waves are oriented in the same direction
Polarization through Transmission:
Created by sending light through certain materials.
Example: ______________
SUNGLASSES 9

10. III. Proof Light is a Wave
Polarization through Reflection:
Light reflects off of surfaces polarized. The reflected polarized light is parallel to the surface
Example: _____________
CAR HOODS 10

11. III. Proof Light is a Wave
B. Diffraction Patterns (animation)
INTERFERNCE
LIGHT
_______________ pattern of ________and ________ fringes caused by wave behavior of light
DARK 11

12. IV. Reflection of Light Law of Reflection:
angle of incidence = angle of reflection
Equation
θ i = θ r 12

13. IV. Reflection of Light Types of Reflection: A) Specular Reflection
Light is reflected off of smooth, shiny surfaces. Rays are ___________ to each other.
PARALLEL 13

14. IV. Reflection of Light Types of Reflection: B) Diffuse Reflection
Reflects light in __________________
VARIOUS DIRECTIONS 14

15. V. Refraction
Refraction: The _________ in direction of a wave as it enters a new _________ at an angle .
CHANGE
MEDIUM
When a (light) wave strikes the interface between two different transparent media, the EM
energy is ___________, ____________, and/or ____________.
REFLECTED
REFRACTED
ABSORBED 15

16. V. Refraction
When a (light) wave is transmitted through a new medium its ____________ changes.
When the material is________________, light _____________
When the material is ________________, light ___________
VELOCITY
MORE “DENSE”
SLOWS DOWN
LESS “DENSE”
SPEEDS UP 16

17. VI. Index of Refraction
Ratio of speed of light in a vacuum to speed of light in a specific material
Equation (see ref. tabs) c
n =
n = index of refraction v
Example: What is the speed of light in corn oil? 17

18. VII. Basic Refraction Diagrams
Snell’s Law Animation
Video Clip
- Bends away from the normal
- v and λ ↑
- f remains constant
- Bends towards the normal
- v and λ ↓
- f remains constant 18

19. VIII. Snell's Law of Refraction
Equation (see reference tables):
n1sinθ1 = n2sinθ2 19

20. VIII. Snell's Law of Refraction
What happens to light when it passes into a new medium that has the same index of refraction as the original?
Beaker Demo (1:30 min) 20

21. VIII. Snell's Law of Refraction
Example: Light, traveling in air, strikes the surface of a diamond at an angle of incidence of 55o. What is the angle of refraction when it enters diamond?
Example: What is the new speed of light when it travels from air into diamond? 21

22. IX. Apparent Depth
One interesting consequence of refraction is that an object lying under water appears to be closer to the surface that it actually is. 22

23. X. Total Internal Reflection
What happens to a beam of light that leaves water and enters air if the angle of incidence is increased? (animation)
Air
(n = 1.00)
Water
(n = 1.33)
Critical angle when θ2 = 90o 23

24. X. Total Internal Reflection
Critical Angle: When angle of incidence is angled so that the angle of refraction equals _______
90o
Equation:
n1sinθ1 = n2sinθ2
At the critical angle, Θ2 = 90o
sinθc = n2 n1
NOTE: Total Internal Reflection only occurs when light is entering a material with a lower index of refraction. Example: From water into air. 24

25. X. Total Internal Reflection
Fiber Optic Cable Demos 25

26. X. Total Internal Reflection
Snell’s Law Animation
Incident ray is completely ___________ back into original medium.
Occurs when:
REFLECTED
2. Angle of incidence is __________
than ________________. θc
GREATER
CRITICAL ANGLE
Whiteboard:
Find the critical angle for diamond (use reference tables) with an air boundary.
A ray of light has an angle of incidence of 30.0o on a block of quartz and an angle of refraction of 20.0o. What is the index of refraction for this block of quartz?
24.4o
1.46 26

27. X. Total Internal Reflection27

28. XI. Dispersion 28

29. XI. Dispersion
Definition: separating (polychromatic) light into separate colors (wavelengths/frequencies)
Uses _______________ to bend light at different angles to separate visible light into various components.
REFRACTION
Red light (longer wavelength) travels faster than violet (shorter wavelength) through the prism, so violet refracts more and appears at the bottom.
Light is dispersed in order of ______________ wavelength.
DECREASING
Index of refraction ultimately depends on the wavelength of light, so every color has a slightly different speed within a substance 29

30. XI. Dispersion Dispersion of Light to form a Rainbow
The red light is refracted out of a droplet at steeper angles towards the ground than the blue light. Thus, when an observer sights at a steeper angle with respect to the ground, droplets of water within this line of sight are refracting the red light to the observer's eye. The blue light from these same droplets is directed at a less steep angle and is directed along a trajectory that passes over the observer's head. Thus, it is the red light that is seen when looking at the steeper angles relative to the ground. Similarly, when sighting at less steep angles, droplets of water within this line of sight are directing blue light to the observer's eye while the red light is directed downwards at a more steep angle towards the observer's feet. This discussion explains why it is the red light that is observed at the top and on the outer perimeter of a rainbow and the blue light that is observed on the bottom and the inner perimeter of the rainbow. (source) 30

31. Why are sunsets red? Why is the sky blue? Video (4 min)
Video (2 min) (3 min)
Why are sunsets red?
Video (4 min) 31

32. XII. Interference of Light
A. Reminders
When a crest and a crest or a trough and trough meet in the same medium ________________ interference occurs. The path difference between the two sources is whole wavelength.
CONSTRUCTIVE
When a trough and crest meet in the same medium _______________ interference occurs. The path difference between the two sources is a half wavelength.
DESTRUCTIVE
The bending of wave (light) around a barrier is called ______________. Draw how the light exits the barrier.
DIFFRACTION 32

34. XII. Interference of Light
B. Young’s Double Slit Experiment
Thomas Young: English Physicist ( )
Proves light is a wave. Shows that light exhibits diffraction and forms an interference pattern when shown on two closely spaced slits.
Suppose Monochromatic light is shown on two closely spaced slits.
CREST MEETS CREST
CREST MEETS TROUGH 34

35. XII. Interference of Light
B. Young’s Double Slit Experiment
Relationships
Wider the barrier opening, smaller the diffraction pattern (decrease in the amount of bending) 35

36. XII. Interference of Light
D. Thin Film Interference 36

37. XII. Interference of Light
D. Thin Film Interference
Reflected light waves off of the top surface interferes with the reflected light waves that travels through the surface. 37