1. Waves and Wave Properties
Presentation for lesson 2: Waves and Wave Properties, in the Waves: The Three Color Mystery unit
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Waves and Wave Properties

2. Why are we able to see?
Answer: Because there is light.
And…what is light?
Answer: Light is a wave (and a particle).
So…what is a wave?

3. Answer: A wave is a disturbance, or vibration, that carries energy from place to place.
A wave does NOT carry matter with it! It just moves the matter as it goes through it.
Think of a stadium wave: the people are moving up and down, but the wave goes around the stadium

4. Some waves do not need matter (called a “medium”) to be able to move (for example, through space).
These are called electromagnetic waves (or EM waves).
Some waves MUST have a medium in order to move. These are called mechanical waves.

5. Wave Types
Transverse waves: Waves in which the medium moves at right angles to the direction of the wave
Sound Waves and Light Waves behave like Transverse Waves

6. Parts of transverse waves:
Crest: the highest point of the wave
Trough: the lowest point of the wave

7. 2. Compressional (or longitudinal) waves: Waves in which the medium moves back and forth in the same direction as the wave
A spring (slinky) or a tuning fork behaves like a compressional or longitudinal wave.

9. Parts of longitudinal waves:
Compression: where the particles are close together
Rarefaction: where the particles are spread apart

10. Wave properties depend on what (type of energy) is making the waves.
Wavelength: The distance between one point on a wave and the exact same place on the next wave.

11. The higher the frequency, the more energy in the wave.
2. Frequency: How many waves go past a point in one second; unit of measurement is hertz (Hz).
The higher the frequency, the more energy in the wave.
10 waves going past in 1 second = 10 Hz
1,000 waves go past in 1 second = 1,000 Hz
1 million waves going past = 1 million Hz

12. Frequency would have units of cycles/second, waves/second, vibrations/second, or something/second.
The unit for frequency is the Hertz (abbreviated Hz) where 1 Hz is equivalent to 1 cycle/second.
The period of a wave is the time for a wave to make one complete cycle.

14. If the woodpecker drums upon a tree 2 times in one second, then the frequency is 2 Hz. Each drum must endure for one-half a second, so the period is 0.5 s.
Therefore the equation between frequency and a period is the following:

15. Rank these waves from highest frequency to lowest frequency by colour; red, blue and purple.

16. 3. Amplitude: How far the medium moves from rest position (where it is when not moving).
Remember that for transverse waves, the highest point is the crest, and the lowest point is the trough.

17. Remember that for compressional waves, the points where the medium is close together are called compressions and the areas where the medium is spread apart are called rarefactions.
The closer together and further apart the particles are, the larger the amplitude.
compression
rarefaction

18. The energy of a wave is proportional to the square of its amplitude
The energy of a wave is proportional to the square of its amplitude. Mathematically speaking . . .
E = A2
Where:
E = energy (the capacity to do work) in Joules
A = amplitude
For example:
If the amplitude is equal to 3 units
E = (3)2 = 9 joules

19. Note that when the amplitude of a wave is one unit, the energy is one unit.
When the amplitude is doubled, the energy is quadrupled.
When the energy is 10 times greater, the energy is 100 times greater!
Amplitude
Energy 1 2 4 3 9 16 5 25 6 36 7 49 8 64 81 10
100

20. Energy, in joules, is also measured by using frequency (v) and Planks Constant. E=(h) (v) Where: E = energy in Joules h = Planks constant 6.626X10-34 v= frequency of the wavelength

21. Example: Calculate the energy of a photon of radiation with a frequency of 8.5 x 1014 Hz. E=hv E=(6.626X10-34)(8.5 x 1014) E=5.63 ×10-19 J

22. Therefore,
The higher the frequency the higher the energy of the wave and,
The higher the amplitude the higher the energy of the wave.

23. A mathematical way to calculate speed:
4. Wave speed: Depends on the medium in which the wave is traveling. It varies in solids, liquids and gases.
A mathematical way to calculate speed:
wave speed = (wavelength) (frequency)
(in meters)
(in Hz) OR
v = (ג)(f)
Problem: If a wave has a wavelength of 2 m and a frequency of 500 Hz, what is its speed?
Answer: speed = 2 m x 500 Hz = 1000 m/s
Answer: speed = 2 m x 500 Hz = 1000 m/s

24. Speed of a wave can also be calculated by: Velocity (m/s) = Distance (m)/time (s)Or
Distance=(Velocity)(Time)
Noah stands 170 meters away from a steep canyon wall. He shouts and hears the echo of his voice one second later. What is the speed of the wave?
v = 170m/1 second
v = 170 m/s

25. Speed of Sound in Different Mediums
Medium velocity m/sec
air (20 C)
air (0 C)
water (25 C)
sea water
diamond
iron
copper
glass

26. Changing Wave Direction
Reflection: When waves bounce off a surface.
If the surface is flat, the angle at which the wave hits the surface will be the same as the angle at which it leaves the surface (angle in = angle out).
This is the law of reflection.
For example, think of a pool ball striking the side of the pool table: The angle it hits the side is the same angle it bounces off the side.

27. 2. Refraction: Waves can bend.
This happens when a wave enters a new medium and its SPEED CHANGES.
The amount of bending depends on the medium it is entering.

28. 3. Diffraction: The bending of waves AROUND an object.
The amount of bending depends on the size of the obstacle and the size of the waves.
Large obstacle, small wavelength = low diffraction
Small obstacle, large wavelength = large diffraction

29. Interference of Wave
Interference of Waves is the phenomenon that occurs when two waves meet while traveling along the same medium.
Two types of interference
1) Constructive 2) Destructive

30. Constructive Interference
1. Constructive Interference - is a type of interference that occurs at any location along the medium where the two interfering waves combine in the same direction. It basically adds energy to the wave.

31. Destructive Interference
2. Destructive Interference – is a type of interference that occurs at any location along the medium where the two interfering waves have a change in the opposite direction. It basically cancels the wave.

32. Electromagnetic Wave Speed in Vacuum 300,000 km/sec or 300,000,000 m/s
c = 3.08X108 m/s
Speed in Other Materials
Slower in Air, Water, Glass
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33. Transverse Waves Moving photon creates electric & magnetic field
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Moving photon creates electric & magnetic field
Light has BOTH Electric & Magnetic fields at right angles!

34. Electromagnetic Spectrum
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35. Electromagnetic Spectrum
1. Visible Spectrum – Light we can see
Roy G. Biv – Acronym for Red, Orange, Yellow, Green, Blue, Indigo, & Violet.
Largest to Smallest Wavelength.
700 nm – 400 nm wavelength

36. Electromagnetic Spectrum
2. Invisible Spectrum
1. Radio Waves (103 – 10-1 m)
Def. – Longest wavelength & lowest frequency.
Uses – Radio & T.V. broadcasting.
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37. Radio Waves
Radio Waves - variation of amplitude or frequency when waves are broadcast
AM – amplitude modulation
Carries audio for T.V. Broadcasts
Longer wavelength so can bend around hills
FM – frequency modulation
Carries video for T.V. Broadcasts

38. 2. Microwaves (10-1 – 10-3 m)
Micro Waves – large to small waves.
They are used in microwaves to heat and cook your food.
They are also used in radars so as to transmit information back and forth.

39. Short Wavelength Microwave
3. Infrared Rays (10-4 – 10-6 m)
Def – Light rays with longer wavelength than red light.
Uses: Cooking, Medicine, T.V. remote controls

40. Electromagnetic Spectrum
3. Ultraviolet rays (10-7 – 10-8 m)
Def. – EM waves with frequencies slightly higher than visible light
Uses: food processing & hospitals to kill germs’ cells
Helps your body use vitamin D.

41. Electromagnetic Spectrum
4. X-Rays (10-8 – m)
Def. - EM waves that are shorter than UV rays.
Uses: Medicine – Bones absorb x-rays; soft tissue does not.
Lead absorbs X-rays.

42. Electromagnetic Spectrum
5. Gamma rays (10-11 – m)
Def. Highest frequency EM waves; Shortest wavelength. They come from outer space.
Uses: cancer treatment.

44. All waves on the Electromagnetic Spectrum (EM spectrum) travel at the speed of light.
Therefore, we need to know one important equation
c = (v)(λ)
Where:
c= speed of light 3.08X108 m/s
v= frequency in hertz
λ=wavelength in meters

45. Example: Violet light has a wavelength of 4. 10 x10-12 meters
Example: Violet light has a wavelength of 4.10 x10-12 meters. What is the frequency? c = (v)(λ) 3.08X108 m/s = (v)(4.10 x10-12 m) v=3.08X108 m/s 4.10 x10-12 m v=7.31 × 1019/s v=7.31 × 1019 Hz

46. LIGHT: Particles or Waves?
Wave Model of Light
Explains most properties of light
But waves cannot move through space (vacuum), so how do Electromagnetic waves move through a vacuum?
Particle Theory of Light
Albert Einstein studies light and suggests that light is a particle.
Electromagnetic waves are photon’s (a particle).
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47. Double Slit Experiment