1. REFLECTION & REFRACTION
Physics

2. Light at Boundaries
When light reaches a new material, two things happen:
Some light bounces back. This is called reflection.
Some light enters (goes through) but turns this is called refraction.

3. Vocabulary Incident wave = the wave that is coming in
Reflected wave = the wave that bounces back
Transmitted wave / Refracted wave = the wave that makes it through

4. How do we measure angles?
Step 1: Draw the normal line (perpendicular to the surface). Step 2: Measure all angles from the Normal.

5. Why do some materials reflect images and others do not?

6. We always measure angles from the NORMAL line!!!
Draw a dotted line that is PERPENDICULAR to the surface. That is called the NORMAL line. All angles are measured from this line. θ

7. LAW OF REFLECTION Incident Angle = Reflected Angle θ1 = θ2
Remember to measure from the normal line. θ1
θ θ θ2
θ θ1

8. PRACTICE: Use similar triangles.
A laser is being held 10 cm above a flat mirror and 25 centimeters in front of it. Meanwhile, the wall is 5 meters away. Where should we place a bull’s eye on the wall in order to catch the laser dot?

9. SOLUTION 10 cm X θ1 θ2 25 cm 5 meters
θ θ2
25 cm meters
We know both triangles have the same angles. So we can use ratios.
= X cross multiply 50 = 25X X = 2 meters high
If we wanted to solve for the angles involved we could use ARC TANGENT. Remember that the incident angle is measured from the normal line!!
In this case the bottom red triangle angle = arctan(10/25) = 22 degrees
This means that the incident angle = 90 – 22 = 68 degrees

10. How does a mirror work? Your brain assumes light goes straight.
Why do mirrors flip horizontally?

11. Miku – World Is Mine https://www.youtube.com/watch?v=O17f3lB7BFY
Show piggy and then Miku.

12. Is light the only wave that reflects?
No. Sound reflections are called echoes.
(Any wave can reflect.)

13. Marching Band Analogy

23. Now let’s try an angled march.

39. Things to Notice The line always turns TOWARDS the slow guy.
When the wave eventually comes back out it is at the same angle it started.

40. Index of Refraction = n Definition:
Tells you how hard it is for light to get through a material
If n = 1 there is no resistance at all. It is as easy as outer space. (air = 1)
If n = 2 then it is twice as hard to get through as outer space. (diamond = 2.4)

41. To calculate the index.
Divide the regular speed of light (300 million) by the speed of light in the new material.
Equation:
n = speed of light in space speed of light in new material
n = c v

42. PRACTICE
Light only moves 226 million m/s in water. What is the index of refraction?

43. Practice
Silicon has an index of How fast does light move in silicon?

44. Predicting Refraction
When light goes from a low index (easy) into a high index (hard) then the wave will turn TOWARDS the normal line. Example is light from my flashlight entering the water.
Index of air = 1
Index of water = 1.33
Fish thinks you are a giant!!

45. Predicting Refraction
When light goes from a high index (hard) into a low index (easy) then the wave will turn AWAY FROM the normal line. Example is light reflecting off a fish and out of the water.
You think the fish is really far away.
Index of air = 1
Index of water = 1.33

46. Physics
Sound

47. Sound Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sound is a longitudinal wave that requires a medium. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Draw this way:
Vibrating Object
Compression:
High pressure
Rarefaction:
Low Pressure

48. Volume Depends on the amplitude of a wave.
Means – How high is the pressure in the high pressure zone?
Measure it using the decibel scale

49. Pitch Depends on the frequency or wavelength.
Means – How many pressure zones hit my ear each second?
Example:
265 Hz is 265 vibrations per second giving us middle C.
High pitched – rapid vibration (Sopranos)
Low pitched – slow vibration (Bass)
Show the pitch forks.

50. Speed of Sound: The speed of sound is: 343 m/s
This is an average depends on air pressure and…

51. Doppler Effect
If the source of a sound is moving the waves will be stretched or compressed accordingly.
If you are getting closer to the source or the source is getting closer to you, you hear a …
If you are moving away from the source or the source is moving away from you, you hear a …
high pitched sound
(because the waves are being compressed.)
low pitched sound
(because the waves are being stretched.)

52. Examples:
Bob is standing in the back of a moving truck while playing the violin. (Do NOT try this at home.) Meanwhile Betty is standing on the top of a moving car driving towards Bob. Bob plays a concert A (frequency = 440 Hz). What frequency (higher or lower than 440Hz) will Betty hear as Bob approaches?
What frequency (higher or lower) will Betty hear as Bob drives away?

53. Examples:
A T-Rex roars at a frequency of 215 Hz. Bob is running away. What sound will Bob hear as he runs? (A high or low frequency?)
Chuck Norris comes running in to take care of the problem. He runs TOWARDS the T-Rex. What sound will Chuck hear? (High or low frequency?)

54. Doppler Effect https://www.youtube.com/watch?v=h4OnBYrbCjY
If you need to replay 1:12 is a good spot to hear the horn again.

55. Doppler Effect and Light
Doppler shift affects the EM spectrum
Emission Spectrum:
Unique colors an element emits.

56. Hydrogen’s Emission Spectrum
Red Shift
Hydrogen’s Emission Spectrum
(Main atom in stars is Hydrogen.)
Red Shift
Shift
If a star moves away from Earth the waves get stretched wider (towards red).

57. Hydrogen’s Emission Spectrum
Blue Shift
Hydrogen’s Emission Spectrum
Blue Shift
Shift
If a star moves towards Earth the waves get compressed (towards blue).

58. Which one is more common?
Red shift (The universe is expanding.)