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# Introduction to Waves

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1. Introduction to Waves

2. The amplitude is the height of the wave. • The wavelength is the distance from one wave top, or crest, to the next. • The Crest is the highest point of the wave • The through is the lowest point of a wave.

3. Check your understanding • What is the lowest point of a wave called? • What is the highest point of a wave called? • What are the units of wavelength? • How do we identify cosine waves?

4. Frequency of Waves

5. Frequency • Frequency is how many waves/second, in units of 1/s or Hertz (Hz)

6. Frequency vs. Wavelength

7. Period vs. Frequency • Period and frequency have an inverse relationship to one another • Frequency is the amount of cycles or waves per second, measured in Hertz • A period is how much time it takes for 1 cycle or wave to pass

8. Check your Understanding • Complete the sentence: The larger the frequency the _______ the wavelength. • Frieda the fly flaps its wings back and forth 121 times each second. The period of the wing flapping is ____ sec. • A period of 5.0 seconds corresponds to a frequency of ________ Hertz. • As the frequency of a wave increases, the period of the wave ___________.

9. Amplitude and Energy of a Wave

10. Amplitude and Energy • a wave is an energy transport phenomenon which transports energy along a medium without transporting matter. • The amount of energy carried by a wave is related to the amplitude of the wave • The energy transported by a wave is directly proportional to the square of the amplitude of the wave. This energy-amplitude relationship is sometimes expressed in the following manner.

11. Check your understanding • Mac and Tosh stand 8 meters apart and demonstrate the motion of a transverse wave on a snakey. The wave e can be described as having a vertical distance of 32 cm from a trough to a crest, a frequency of 2.4 Hz, and a horizontal distance of 48 cm from a crest to the nearest trough. Determine the amplitude, period, and wavelength of such a wave. • An ocean wave has an amplitude of 2.5 m. Weather conditions suddenly change such that the wave has an amplitude of 5.0 m. The amount of energy transported by the wave is __________. a. halved b. doubled c. quadrupled d. remains the same

12. Wave Speed

13. Wave Speed • Speed = wavelength x frequency v=fλ • Units are in meters/second • Waves carry energy and NOT matter

14. Check your understanding • Does the medium in which the wave travels move with the wave? • What’s your formula for wave speed? • As a water wave passes by, a portion of water vibrates up and down 2 complete cycles in 1 second. What is the wave’s speed for a wave of length 5 meters? • The sound from a 60 Hz electric razor spreads out at 340 meters per second, what is its frequency? Period? Speed? wavelength?

15. Complete the table below

16. CATEGORIES OF WAVES

17. Longitudinal vs. Transverse • One way to categorize waves is on the basis of the direction of movement of the individual particles of the medium relative to the direction which the waves travel

18. Longitudinal vs. Transverse • A transverse wave is transporting energy from east to west. The particles of the medium will move_____. • A wave is transporting energy from left to right. The particles of the medium are moving back and forth in a leftward and rightward direction. This type of wave is known as a ____.

19. Mechanical vs. Electromagnetic • Another way to categorize waves is on the basis of their ability or inability to transmit energy through a vacuum (i.e., empty space). • Electromagnetic waves can travel through a vacuum (empty space) • Mechanical waves cannot travel through empty space

20. Electromagnetic waves • All light waves are examples of electromagnetic waves • An electromagnetic wave is a wave which is capable of transmitting its energy through a vacuum (i.e., empty space). Electromagnetic waves are produced by the vibration of charged particles. • Electromagnetic waves which are produced on the sun subsequently travel to Earth through the vacuum of outer space. Were it not for the ability of electromagnetic waves to travel to through a vacuum, there would undoubtedly be no life on Earth.

21. Electromagnetic Spectrum

22. Mechanical Waves • Examples of mechanical waves: slinky waves, water waves, stadium waves, and sound • A mechanical wave is a wave which is not capable of transmitting its energy through a vacuum • Mechanical waves require a medium in order to transport their energy from one location to another. Sound waves are incapable of traveling through a vacuum

23. Check your understanding • A science fiction film depicts inhabitants of one spaceship (in outer space) hearing the sound of a nearby spaceship as it zooms past at high speeds. Critique the physics of this film. • Which of the following is not a characteristic of mechanical waves? a. They consist of disturbances or oscillations of a medium. b. They transport energy. c. They travel in a direction which is at right angles to the direction of the particles of the medium. d. They are created by a vibrating source. A sound wave is a mechanical wave; not an electromagnetic wave. This means that a. particles of the medium move perpendicular to the direction of energy transport. b. a sound wave transports its energy through a vacuum. c. particles of the medium regularly and repeatedly oscillate about their rest position. d. a medium is required in order for sound waves to transport energy

24. Transverse Waves

25. Transverse Waves • Examples (light, ocean, all electromagnetic waves, seismic waves) • In transverse waves, the molecules of the medium oscillate perpendicular to the direction of propagation

26. Electromagnetic Spectrum(Transverse Wave)

27. Electromagnetic Waves • An Electromagnetic wave can travel through a vacuum, how else would sunlight travel through space and reach the earth? • An electromagnetic wave is a wave of energy produced when an electric charge accelerates. • Light accelerates from the accelerated motion of electrons. • IN A VACUUM- all electromagnetic waves move at a speed of 3.0 x 108 meters/sec

28. Check your understanding • Is it correct to say that radio waves are a low-frequency light wave? Is a radio wave also a sound wave? • What is the principal difference between a radio wave and light? Between light and X-rays?

29. Electromagnetic Spectrum • Electromagnetic waves exist with an enormous range of frequencies. This continuous range of frequencies is known as the electromagnetic spectrum.

30. Visible light Spectrum • the very narrow band of wavelengths located to the right of the infrared region and to the left of the ultraviolet region. • Though electromagnetic waves exist in a vast range of wavelengths, our eyes are sensitive to only a very narrow band. Since this narrow band of wavelengths is the means by which humans see, we refer to it as the visible light spectrum • When all the wavelengths of the visible light spectrum strike your eye at the same time, white is perceived.

31. Check your understanding • A light wave is an electromagnetic wave which has both an electric and magnetic component associated with it. Electromagnetic waves are often distinguished from mechanical waves. The distinction is based on the fact that electromagnetic waves ______. a. can travel through materials and mechanical waves cannot b. come in a range of frequencies and mechanical waves exist with only certain frequencies c. can travel through a region void of matter and mechanical waves cannot d. electromagnetic waves cannot transport energy and mechanical waves can transport energy e. electromagnetic waves have an infinite speed and mechanical waves have a finite speed

32. Check your Understanding Consider the electromagnetic spectrum as you answer these three questions. a. Which region of the electromagnetic spectrum has the highest frequency? b. Which region of the electromagnetic spectrum has the longest wavelength? c. Which region of the electromagnetic spectrum will travel with the fastest speed? • Consider the visible light spectrum as you answer these two questions. a. Which color of the visible light spectrum has the greatest frequency? b. Which color of the visible light spectrum has the greatest wavelength?

33. Longitudinal Waves

34. Longitudinal Waves • Examples: Sound, seismic P-waves , • Longitudinal waves are waves that have vibrations along or parallel to their direction of travel; that is, waves in which the motion of the medium is in the same direction as the motion of the wave. • The speed of a longitudinal wave depends upon the medium through which it travels through

35. Sound • Sound is a longitudinal wave • Sound is a mechanical wave • Sound is a pressure wave

36. Sound Waves • Sound waves in air (and any fluid medium) are longitudinal waves because particles of the medium through which the sound is transported vibrate parallel to the direction which the sound wave moves • Sound waves are mechanical waves because it needs a medium to travel through, cannot travel through empty space • Since a sound wave consists of a repeating pattern of high pressure and low pressure regions moving through a medium, it is sometimes referred to as a pressure wave

37. Sound Waves • Speed of Sound depends on the material which it propagates. • Material • Rubber60 m/s • Air at 40oC355 m/s • Glass4540 m/s • Lead1210 m/s • Stone5971 m/s • Copper3100 m/s • What happens when you change the material through which the sound travels? • Through which material does sound move faster? Why do you think it is faster?

38. Sound and Pitch (frequency) • Frequency of sound is described as pitch • A high-pitch sound (like a tiny bell) has a high frequency • A lower-pitch sound ( like a church bell) has a low frequency • The human ear can hear pitches from 20Hz - 20,000 Hz

39. Check your understanding • A singer sings a high-pitch note and then a low-pitch note. For which note are her vocal chords vibrating faster? Which note sets the air into higher frequency vibrations? • Can sound travel through a vacuum? Why or why not?

40. Check your understanding • A sound wave is different than a light wave in that a sound wave is a. produced by an oscillating object and a light wave is not. b. not capable of traveling through a vacuum. c. not capable of diffracting and a light wave is. d. capable of existing with a variety of frequencies and a light wave has a single frequency.

41. Check your Understanding • A sound wave is a pressure wave; regions of high (compressions) and low pressure (rarefactions) are established as the result of the vibrations of the sound source. These compressions and rarefactions result because sound a. is more dense than air and thus has more inertia, causing the bunching up of sound. b. waves have a speed which is dependent only upon the properties of the medium. c. is like all waves; it is able to bend into the regions of space behind obstacles. d. is able to reflect off fixed ends and interfere with incident waves e. vibrates longitudinally; the longitudinal movement of air produces pressure fluctuations.

42. Review

43. Visit this website • Take quiz on this website http://glencoe.mcgraw-hill.com/sites/dl/free/0078778115/161383/00053404.html • Take this quiz on this website http://library.thinkquest.org/C005705/English/Waves/quiz.htm

44. Properties of waves