1. WAVES Chapter 15

2. TYPES OF WAVES Section 1 2

3. WAVES Wave: a movement of energy with no net movement of matter. Like the wave done at a football game. The fans stand up and sit back down, no net movement (they end up where the started). However, the wave itself actually moves around the stadium. 3

4. WAVES Medium: any substance a wave can travel through (plural is media) Mechanical Waves: require a medium Examples include sound or water waves Most waves are mechanical Electromagnetic Waves: waves that can travel without a medium, but will travel through one if it is there. Examples include radio waves, light, IR, and UV Consist of changing electric/magnetic fields in space, which means they can travel through outer space without a medium. 4

5. WAVES & ENERGY Energy: ability to exert force over a distance (or to do work) Waves can do work, like moving a boat on the water The bigger the wave, the more energy Tsunamis carry a lot of energy Tsunamis 5

6. WAVES & ENERGY When waves travel, the energy spreads The waves spread out in circles called a wave front Each wave front carries the same amount of energy, but they spread it out over a larger area This is why people farther from an earthquake don’t feel the earth move as much 6

7. VIBRATIONSVIBRATIONS & WAVES Most waves are caused by vibrating objects When a singer sings, the vocal cords vibrate Electromagnetic waves are caused by the vibration of charged particles Mechanical waves are caused by the vibrating particles of a medium 7

8. TRANSVERSE WAVES Transverse Wave: wave motion is perpendicular to the particle motion Electromagnetic waves are transverse waves Imagine “the wave” at a sporting event The particles, or people, in the wave move up and down The wave itself moves left to right around the stadium 8

9. TRANSVERSE WAVES 9

10. LONGITUDINAL WAVES Longitudinal Waves: the particles of the medium vibrate parallel to the direction the wave is moving. Sound waves are longitudinal waves Compression: When the particles are compressed together Rarefaction: When the particles are spread out 10

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12. SURFACE WAVE Surface Waves: Waves occurring at the boundary of two media that combine both transverse and longitudinal waves. The surface of water does this. The air is longitudinal, the water underneath is transverse, causing the water molecules to move in a circle. 12

13. CHARACTERISTICS OF WAVES Section 2 Science 360: Giant Shake Table Earthquake Simulator

14. AMPLITUDE & WAVELENGTH Amplitude: the height of the wave (compared to the original resting position); measures the amount of particle vibration The larger the amplitude of the wave, the more energy it has. Wavelength: The distance between two equivalent parts of a wave Crest to crest, trough to trough, rarefaction to rarefaction, compression to compression 14

15. AMPLITUDE & WAVELENGTH Both are a measure of distance and both tell you about energy The larger the amplitude, the more energy The shorter the wavelength, the more energy 15

16. PERIOD & FREQUENCY Period: time it takes for one wave to pass from crest to crest or trough to trough (one full cycle) Basically, the number of seconds between two successive wave crests (two “ups”, or two “downs”) Units are seconds, represented by T 16

17. PERIOD & FREQUENCY Frequency: number of cycles or waves per second Units are hertz (Hz) Represented by f Example on right: Same amount of time, but different number of “cycles” 17

18. WAVE SPEED Wave Speed: The rate of travel of a wave Units are m/s, represented by v The speed of a wave depends on the medium Sound waves travel fast through air, faster through water, and fastest in solids Remember the Kinetic Theory - solids, liquids, gases are constructed differently The more molecules, the better the movement of the wave 18

19. PITCH Pitch: how high or how low a sound is Determined by frequency (how fast the vibrations travel) Frequency changes when the wave source waves is moving The closer the noise making object is, the more frequent; the further away the less frequent the wave 19

20. THE DOPPLER EFFECT Motion between the source of waves and the observer creates a change in observed frequency You’ve experienced this with an ambulance passing by 20

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22. WAVE INTERACTIONS Section 3

23. WAVE INTERACTIONS When a wave comes into contact with a different medium (like air to water, air to glass etc.) it can - be reflected (bounced back) pass through the object, or be absorbed convert to another form of energy Normally it does some measure of all 3 23

24. WAVE INTERACTIONS Reflection: When a wave meets a surface or boundary and it bounces back Diffraction: When waves bend around an object or opening This is why we can hear voices in a room when we are standing outside the door Refraction: The bending of a wave when it passes from one medium to another 24

25. INTERFERENCE What happens when two waves collide with one another? Interference: When several waves share the same location, they combine to produce a single, new wave that is different than the original waves 25

26. INTERFERENCE Constructive Interference: When two waves overlap and they reinforce each other The result is a wave with an amplitude of the two waves combined 26

27. INTERFERENCE Destructive Interference: When two waves overlap and the crest of one wave meets the trough of another wave The amplitudes subtract from each other and the wave produced has a smaller amplitude 27

28. INTERFERENCE When light waves bounce off a bubble, some waves bounce right back, some waves go through, the colors you see are determined by the interference of the waves When interference of sound waves occurs, a beat is produced Science 360: Sounds of Nascar 28

29. INTERFERENCE Standing Wave: Interference between a wave and its reflection Nodes: points where there is no vibration Maximum destructive interference at this point. Antinodes: points with the most vibration. Maximum constructive interference at this point. 29

30. SOUND & LIGHT Chapter 16 – Sections 2 and 3

31. THE NATURE OF LIGHT Section 2 31

32. LIGHT Light is a form of energy The energy is proportional to its frequency Light is considered to have a dual nature – which means it can act as a particle and a wave Both models are currently accepted and can be correct depending on the experiment! 32

33. WAVE MODEL Shown by Thomas Young Describes light as a transverse wave (has amplitude, frequency and wavelength) that doesn’t require a medium Light waves are also called electromagnetic waves because they consist of changing electric and magnetic fields 33

34. PARTICLE MODEL Photons: packets, or units, of light A beam of light is a stream of photons If light carries particles (photons) then this can account for the electrons bouncing off the metal plate Photons do not have mass, they are like little bundles of energy located in a specific area 34

35. INTENSITY The brightness of light depends on intensity Intensity depends on the number of photons per second, or power, that pass through a certain area of space Intensity of light decreases as distance from the light increases 35

36. SPEED OF LIGHT Speed of light (a wave) is a constant value c = 3.00 x 10 8 m/s (or 186,000 miles/second) The speed of light depends on the medium Differences in the frequency of light explain why we can see differences in color 36

37. ELECTROMAGNETIC SPECTRUM Electromagnetic Spectrum: the full range of light at different frequencies Consists of waves at all possible energies, frequencies, and wavelengths (not all are visible to us) 37

38. RADIO WAVES Radio Waves: longest in the spectrum Wavelengths from tenths of a meter to thousands of meters TV signals, radio signals Radar: a system that uses radio waves to find the locations of objects The waves bounce off the object and return to a receiver Airplanes use this, policemen 38

39. MICROWAVES Used in cooking and communication Wavelengths in range of centimeters Reflected by metals, transmitted through air, glass, paper and plastic The water, fat and sugar in foods absorb microwaves 39

40. INFRARED LIGHT Slightly longer wavelengths of red visible light Can be felt as warmth From the sun Used to warm food at restaurants Used in sensors to measure heat energy 40

41. ULTRAVIOLET LIGHT Invisible light that lies just beyond violet light Higher energy and shorter wavelengths than visible light Many insects can see but not humans 41

42. X RAYS AND GAMMA RAYS X Rays Higher energy and shorter wavelengths than UV waves Gamma Rays EM waves with the highest energy and have very short wavelengths Both used in medicine 42

43. REFLECTION & COLOR Section 3

44. REFLECTION OF LIGHT Every object reflects some light and absorbs some light Light Ray: imaginary line running in the direction the light travels Direction of the light ray is the same as the direction of wave travel in the wave model, or as the path of photons in the particle model This model of light is useful for showing how light behaves in various situations 44

45. REFLECTION OF LIGHT How light is reflected/absorbed depends on the surface of the object Rough surfaces reflect the light in many directions Diffuse Reflection: reflection of light into random directions 45

46. REFLECTION OF LIGHT Smooth surfaces reflect in one direction Angle of Incidence: the angle at which the light hits the surface Angle of Reflection: the angle of light rays reflecting off the surface Law of Reflection: (the equality of the two above angles) the angle of incidence equals the angle of reflection 46

47. MIRRORS Mirrors reflect light as described by the law of reflection, and this light reaches your eyes The type of image received depends on the type of mirror Flat mirrors form virtual images by reflection When the reflected light reaches your eyes, you see an image of the object behind the mirror It appears to be as far behind the mirror as you are in front of the mirror 47

48. MIRRORS Curved mirrors distort images The line of reflection is not straight Convex Mirrors: curve out (like side mirrors on the car) and make images appear smaller Concave Mirrors: curve in, some magnify objects 48

49. COLOR The colors that you perceive depend on the wavelengths of visible light that reach your eyes Like a leaf, it only reflects light, doesn’t emit light Objects have the color of the wavelengths they reflect Mixtures of colors produce other colors 49