WAVES

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NATURE OF WAVES Waves (Def.) – A wave is a disturbance that transfers energy. Medium – Substance or region through which a wave is transmitted. Speed of Waves – Depends on the properties of the medium. © 2000 Microsoft Clip Gallery

4 Waves transfer energy such as sound, heat, light, and earthquakes through different mediums Energy has the potential to exert a force over a distance Sound and light waves allow organisms to "hear" and "see" the world around them Relate the energy of a wave to wavelength

What is a wave? Mechanical Wave: –w–when materials oscillate (move back in forth) to transfer energy. It needs to have an initial energy input and a medium in which to travel. What do waves transfer then? Energy! Medium – –T–The substance the wave travels through, can be gas, liquid, or solid

What causes waves? Vibration – are the oscillations that occur in a wave. A waves frequency equals the frequency of the vibrating source producing the wave.

Types of waves Transverse waves – move side to side (Light Waves) –Parts: Crest – the top part of the wave Trough – the bottom part of the wave

8 Longitudinal waves – move in and out by compressing together (Sound Waves) –Parts Compression – close together Rarefaction – far apart Compression Rarefaction

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Basic wave properties I All waves have 4 basic properties –Amplitude – maximum amount of displacement from the medium at rest; the height –Wavelength – the length of one complete cycle Amplitude Wavelength

Basic Wave Properties II Frequency – how often the wave occurs over a period of time. –C–Cycles per second. Measured in Hertz (Hz) –E–Example: 8 cycles in 2 seconds = 4 Hz Speed – the meters the wave traveled per second –S–Speed = 9 meters in 3 seconds = 3 m/s Speed = wavelength x frequency

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1. A wave has a wavelength of 15 cm and has a frequency of 10 waves/second. What is the speed of the wave? 2.The speed of a wave on a rope is 50cm/s and it’s wavelength is 10cm. What is it’s frequency? 3.A wave is traveling with a velocity of 125m/s and has a frequency of 20 waves/second. What is the length of the wave? Speed = Wavelength x Frequency

15 Now get your slinky again! Get with the same partner as before. Lay your slinky on the ground or table. You hold one end while your partner holds the other. Make a transverse wave. Now make a longitudinal wave. Now pick one of the waves and add a lot of energy. Describe your wave _______ ___________________________________ ________ Now stay with the same type of wave and add just a small amount of energy. Describe your wave ___________________________________ __ ______________________________.

16 The more energy a wave has, the greater its amplitude and smaller its wavelength. Which wave has a greater frequency… one with a long wavelength or a short wavelength? Which wave has a higher energy… one with a long wavelength or a short wavelength?

17 Wave Speed A Greater Speed means either: A greater Frequency – Or A greater wavelength

18 What Is Sound?  Sound is vibrations that you can hear  Sound travel as longitudinal waves  Sound is due to vibrations that make the molecules around them compress. Ex: Air particles are compressed and spread out Travel at 343 meters/second

19 Sound Depends On:  A vibrating source to set up the sound waves  A medium to carry the waves  A receiver to detect them

20 Sound Vibrations  Back-and-forth movement of matter or particles of matter  Sound travels away from the vibrating object in all directions until it reaches a surface where it is absorbed or reflected.

21 Sound waves travel at all directions until it reaches a surface where it is absorbed or reflected.  This is how sound waves normally travel from one source.

22 Reflection vs. Absorption  Just like light waves, sound waves can be reflected or absorbed  Sound waves reflect straight from a smooth, flat surface There is a clear echo There is a clear echo  Sound waves are reflected in many directions from a rough, uneven surface There is no clear echo There is no clear echo

23 Can sound travel in empty space??  No! Because there is no medium or particles. Light may travel through space because it is a particle that Travels in a Wave and Thus does not Need a medium.

24 Sound waves from a tuning fork.  As the fork vibrates it causes particles to compress and rarefact (spread out)

25 Volume: Intensity/Loudness  Amount of sound energy reaching your ears  Or: How High the Amplitude is  Depends on: How far the vibrating object is moving as it goes back and forth How far the vibrating object is moving as it goes back and forth How far you are from the source of a sound How far you are from the source of a sound Volume Control

26Pitch The Higher the Frequency the Higher the Pitch. The Lower the Frequency the Lower the Pitch.  Depends on how fast the source of the sound is vibrating  To change the pitch: Change the length of the material vibrating Change the length of the material vibrating Change the thickness of the material vibrating Change the thickness of the material vibrating Example: Boom WhackersExample: Boom Whackers

27 Name that Tune  C C C G A A G  E E D D C  The different lengths will cause a higher frequency or vibration when struck OR A lower frequency when longer because it makes a longer wavelength.

28 Sound Travels at Different Speeds Through Different Materials  Feet per second

29 Which Would Be the Best Conductor?  Solid?  Liquid?  Gas?  Solid – The Bricks!

30 What happens to the speed of sound if the temperature changes?  For the answer visit the following website:  Why does this happen? Molecules move faster as the temperature increase and slower as the temperature decreases Molecules move faster as the temperature increase and slower as the temperature decreases Because Air is the medium at which sound travels it affects the speed. Because Air is the medium at which sound travels it affects the speed. If the temperature is the same, then the speed of sound is the same on a mountian top or at ocean level If the temperature is the same, then the speed of sound is the same on a mountian top or at ocean level Air Pressure and Air Density DO NOT affect speed of sound.Air Pressure and Air Density DO NOT affect speed of sound. Density of Materials (solids, liquids, gases) does matter!Density of Materials (solids, liquids, gases) does matter!

31 Doppler Affect  Occurs as sound is made from a moving source  Occurs as sound travels away from you or toward you.  Pitch is heard because  Toward: higher pitch  Away: lower pitch

32  Ultrasound or ultrasonography is a medical imaging technique that uses high frequency sound waves and their echoes. The technique is similar to the echolocation used by bats, whales and dolphins, as well as SONAR used by submarines. In ultrasound, the following events happen: submarines

33 The ultrasound machine transmits high-frequency (1 to 5 megahertz) sound pulses into your body using a probe.  The sound waves travel into your body and hit a boundary between tissues (e.g. between fluid and soft tissue, soft tissue and bone).  Some of the sound waves get reflected back to the probe, while some travel on further until they reach another boundary and get reflected. reflected  The reflected waves are picked up by the probe and relayed to the machine. The machine calculates the distance from the probe to the tissue or organ (boundaries) using the speed of sound in tissue The machine displays the distances and intensities of the echoes on the screen, forming a two dimensional image like the one shown below.

34SONAR  To locate a target, a submarine uses active and passive SONAR (sound navigation and ranging). Active sonar emits pulses of sound waves that travel through the water, reflect off the target and return to the ship. By knowing the speed of sound in water and the time for the sound wave to travel to the target and back, the computers can quickly calculate distance between the submarine and the target Whales, dolphins and bats use the same technique for locating prey (echolocation).

35 As Sound Breaks the Sound Barrier it creates a loud boom!  Occurs when travel faster than the speed of sound: 343 m/sec.  This is because air particles can’t move out of the way fast enough.

36 When something travels faster than sound> Supersonic  Because air particles don’t move out of the way it creates an additional wave.

37 Making Glasses Sing  As the resonant wave moves around the glass, it drags the water molecules with it, creating a wave of water that you can see near the edge of the glass. The dragging water molecules effectively increase the mass (both the water and the glass molecules) and reduce the energy of the wave traveling through the glass. When the energy is reduced, so is the frequency of the wave in the glass, which is reflected in the pitch of the sound wave that you hear.  As you add more liquid in there is more vibrating material and you get a lower frequency and a lower pitch. uestion603.htm

SAMPLE LESSON: Light & the Electromagnetic Spectrum By D. L. Power Revised 1/20/01 © 2000 Microsoft Clip Gallery

LIGHT: What Is It? Light Energy –Atoms As atoms absorb energy, electrons jump out to a higher energy level. Electrons release light when falling down to the lower energy level. –Photons - bundles/packets of energy released when the electrons fall. Light: Stream of Photons This photon travels in a wave. © 2000 Microsoft Clip Gallery

Electromagnetic Waves Speed in Vacuum –300,000 km/sec –186,000 mi/sec Speed in Other Materials –Slower in Air, Water, Glass © 2000 Microsoft Clip Gallery

Electromagnetic Spectrum © 2000 Microsoft Clip Gallery

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

LIGHT: Refraction of Light Refraction – Bending of light due to a change in wave speed. –Index of Refraction – Amount by which a material refracts light. –Prisms – Glass that bends light. Different frequencies are bent different amounts & light is broken out into different colors.

It is (mainly) reflected or refracted ? away from or towards the normal the normal What happens to the ray of light? But different colours are refracted by different angles.

In fact, the ray is : (bent through an angle), and devi ated dispersed (split up into separate colours) like this.

What happens now? R V screen Red is deviated most / least ? Violet is deviated most / least ? least most

R V screen There is a spectrum on the screen: Red Orange Yellow Green Blue Indigo Violet ROY G BIV

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