1. Waves and Wave Properties
Chapter 11
Waves and Wave Properties

2. What is a Wave? Rhythmic disturbance that transfers energy
Several types of waves
Water
Sound
Earthquakes – seismic waves
Light

3. What do waves travel through?
The medium is stuff a wave travels through
Water
Sound has air as a medium
Earthquakes have the earth as a medium
Mechanical waves are those that require a medium

4. Light Doesn’t require a medium
Made up of waves of electrical and magnetic forces
Called electromagnetic waves
Many types of these waves
Radio
Microwaves
Ultraviolet
Book uses “light” for all of these

5. Energy Waves transfer energy Ocean waves move objects up and down
Sound waves move your eardrum in and out
Light makes molecules vibrate faster.

6. Waves Spread Out As they travel, waves get wider
Don’t create or destroy energy
So there is less energy transferred in any given spot
Lights get dimmer the further away
Headphones aren’t as loud as speakers
Speakers need amplifier

8. Vibrations Most waves are caused by vibrations Vocal cords Strings
Light is caused by vibrating electrons

9. Types of Waves
Transverse
Longitudinal
Surface

10. Transverse Waves Trans – means across
Matter moves at right angles to the direction the wave travels
As the energy moves forward, the wave goes up and down
Ex: The wave at a football game.

11. Longitudinal Waves Energy and waves move the same direction
Move parallel
Particles squeezed together then move apart
Sound Waves

13. Surface Waves Occur at boundary between two mediums
Particles move in circles, energy moves forward
Combination of transverse and longitudinal waves

14. Water Wave Rayleigh Surface Wave
Another example of waves with both longitudinal and transverse motion may be found in solids as Rayleigh surface waves. The particles in a solid, through which a Rayleigh surface wave passes, move in elliptical paths, with the major axis of the ellipse perpendicular to the surface of the solid. As the depth into the solid increases the "width" of the elliptical path decreases. Rayleigh waves are different from water waves in one important way. In a water wave all particles travel in clockwise circles. However, in a Rayleigh surface wave, particles at the surface trace out a counter-clockwise ellipse, while particles at a depth of more than 1/5th of a wavelength trace out clockwise ellispes. The movie below shows a Rayleigh wave travelling from left to right along the surface of a solid. I have identified two particles in blue to illustrate the counterclockwise-clockwise motion as a function of depth.

15. Transverse Waves

16. Parts of Wave Crest – high point on a wave
Trough – Low point on a wave
Amplitude – distance it rises or falls from rest position
Depends on the energy in the wave
Wavelength – distance from the crest to crest (one whole wave)

17. Parts of a Wave
Figure 1: White line represents the position of the medium when no wave is present.
Yellow line represents the position of medium as a wave travels through it (the wave)
Often, when several waves are traveling along a medium as shown above, the continuous group of waves is called a wave train.
Crest and Trough: The section that rises above the undisturbed positions is called the crest. The section that lies below the undisturbed position is called the trough.

18. The term amplitude can have slightly different meanings depending on the context of the situation.
General Definition: Amplitude is the maximum positive displacement from the undisturbed position of the medium to the top of the crest.

19. In some discussions it is important to distinguish between positive and negative amplitudes.
Sometimes it is necessary to discuss an amplitude at a certain point along the wave. Several of these amplitudes are shown in the following diagram. Notice: 3 are positive amplitudes and 2 are negative.

20. Other Examples
Wavelength

21. http://id. mind. net/~zona/mstm/physics/waves/partsOfAWave/waveParts

22. Frequency of a Wave Number of waves that go by a point in one second
How fast it goes up and down
Longer wave, lower frequency
Shorter wave, higher frequency
Units are hertz (Hz)
1 hertz is one wave per second, or one cycle per second

23. Velocity of a Wave Depends on wavelength and frequency
Velocity = wavelength x frequency
Calculate the velocity of a wave with a wavelength of 10m and a frequency of 325 Hz

24. Electromagnetic Spectrum
The kind of waves that make light also make radio, radar, infrared, gamma rays, X-rays, microwaves, UV
The arrangement of these in order of wavelength and frequency is the electromagnetic spectrum
Can be produced by electricity or magnetism

26. X-rays Discovered by Roetgen Made when electrons hit tungsten
Cause phosphorus to glow
Shorter wave, higher frequency
Affect film
Pass through all materials to some extent
Depends on density
More dense (bone) blocks X-rays

27. Ultraviolet Radiation
Higher energy wave than light
Shorter wave, higher energy
Skin uses it to make Vitamin D
Causes skin cancer
Black light
Fluorescent objects absorb UV, then gives it off as light.

28. Infrared Longer wavelength than light, lower energy
Given off by objects when they are warm
Used in heat seeking missiles
By energy power companies to detect heat

29. Microwaves Longer than infrared (lower energy)
Used for communication (telephone)
Microwave oven uses microwaves turned to frequency of water molecules
Make them resonate
Heat them up

30. Radio Longer waves than microwaves Two types AM Amplitude Modulated
Sends sound by changing the amplitude
Reflected by ionosphere to travel long distances

31. Radio FM Frequency Modulated
Sends the signal by changing the frequency
Less affected by atmosphere – less noise
Do not bounce off ionosphere
Don’t travel as far (80km)

32. Radio – How it Works
Microphone turns sound waves into electrical signal
Amplified then sent as radio waves by antenna
Go through air to antenna
Receiver turns radio signal to electricity
Amplified and sent to speaker
Speaker turns electricity to sound

33. Television Sends pictures as well as sound
Works like radio, except it turns light to FM waves

34. Waves are fun!