WAVES 1
How are waves generated? Waves are generated by 2
Wave a disturbance that transmits energy through empty space or through a medium Medium any solid, liquid, or gas 3
Types of Waves 1. Electromagnetic consists of oscillating electric and magnetic fields a. Requires no medium b. Ex: light, X-rays, radio, gamma rays 4
Types of Waves 2. Mechanical energy transferred from one particle of a medium to the next a. Medium required b. Ex: sound, water waves c. 2 types: transverse & longitudinal 5
Wave Topics A. Period (p. 516) B. Frequency (p. 516) C. Wave Speed (p. 518-521) D. Transverse Waves (p. 511) E. Longitudinal Waves (p. 512) F. The Parts of a Wave (p. 512, 514-515) 6
What type of mechanical wave is this? TRANSVERSE
Transverse Wave Wave moves perpendicular to the particles of the medium 8
Transverse Wave CREST AMPLITUDE WAVELENGTH TROUGH
What type of mechanical wave is this? Animation http://www.kettering.edu/physics/drussell/demos/waves/wavemotion.html 11
Longitudinal Wave Wave moves parallel to the particles of the medium http://www.kettering.edu/physics/drussell/demos/waves/wavemotion.html 12
Longitudinal Wave COMPRESSION RAREFACTION WAVELENGTH
Longitudinal Wave
Frequency Period # of waves/time time/wave Hertz (Hz) Seconds (s) 1 f T
Wave Speed Depends on the medium Wave speed = frequency x wavelength v: velocity (m/s) v f: frequency (Hz) l f l l: wavelength (m) T: period v T
What are two types of mechanical waves? Longitudinal Transverse 18
Review What are the key parts of the following wave? What are the appropriate units for frequency? Frequency is the number of waves that pass a point each second. It is measured in Hertz (Hz). 19
Wave Sample Problems Calculate the speed of waves in a puddle that are 0.650 m apart and made by tapping the water surface 5 times each second. 20
Wave Sample Problems Crickets produce a chirping sound based on the outside temperature. Some chirps can have wavelengths in air of 1.25 m. If the speed of sound in air is 346 m/s, what is the frequency of the chirp produced by a cricket? What is its wave period?
Wave Sample Problems A manatee can typically hear sounds with frequencies up to 32,000 Hz. What is the speed of sound in water if a wave with this frequency has a wavelength of 10 cm. (Hint: Convert cm to meters.) 22
Wave Sample Problems A buoy bobs up and down in the ocean. The waves have a wavelength of 6.3 m, and they pass the buoy at a speed of 12.8 m/s. What is the frequency of the waves? How much time does it take for one wave to pass under the buoy? (Hint: Find the wave period.)
Wave Practice Problems, Part 2 check your answers 3) 0.0076 m 4) 10 s 5) 0.0136 m 6) 38 m 7) 1.6 m/s 8) 129 Hz 0.0078 s 9) 15000 m/s 10) 1.6 Hz 0.625 s
Review What are the key parts of the following wave? What is the appropriate unit for wave period? 1. Quiz Review 2. Group Review Game Wave period is the amount of time it takes for one wave to pass a given point. It is measured in seconds (s). 25
ENERGY A wave is disturbance that transmits ELECTROMAGNETIC waves consists of oscillating electric MEDIUM and magnetic fields and do not require a. ALL FORMS AND COLORS OF LIGHT Examples include. MECHANICAL waves must have a medium because the energy is transferred from through the particles. LONGITUDINAL There are two types of this wave and TRANSVERSE. 26
CREST AMPLITUDE WAVELENGTH TROUGH
The time it takes for one wave to pass a point is called WAVE PERIOD (T) The number of waves that pass in one second is called FREQUENCY (F) These variables are reciprocals (inverse) of each other. T= 1/F or F= 1/T 29
AFTER THE QUIZ WAVE BEHAVIORS GUIDED READING
Electromagnetic Spectrum
The Electromagnetic Spectrum
Electromagnetic Waves Vibrating magnetic & electric fields Can travel through a vacuum v = 3.00 x 10 8 m/s (in a vacuum)
The Electromagnetic Spectrum
Radio Waves Lowest frequency Longest wavelength Radios, TVs, cell phones
Microwaves Used in cooking (microwave oven) Food absorbs wave Energy from wave converts to heat
Infrared heat waves Uses: keeping food warm, animal tracking, infrared photography http://coolcosmos.ipac.caltech.edu/image_galleries/our_ir_world_gallery.html
Visible Light Different frequencies seen as different colors ROYGBIV Red: lowest frequency, least energy Violet: highest frequency, most energy
Ultraviolet Higher frequency than light More penetrable Causes sunburns, damages tissue, kills bacteria
X-Rays High energy Can penetrate soft tissue Uses: medical tests, checking luggage at airport
Gamma Rays High frequency, short wavelength High energy Produced by nuclear particles Used in radiation treatment to kill cancer cells
Draw a transverse wave and label the amplitude. Wave Behaviors Discussion Wave Behaviors lab Lab Explanations
Wave Behaviors Reflection Refraction Diffraction Interference
Wave Behaviors Reflection Bounces off boundary Refraction The bending of a wave as it moves from one medium to another Diffraction The bending of a wave around a barrier
Reflection
Refraction
Diffraction
Interference The combining of 2 waves Two types: Constructive Destructive
Constructive Interference
Destructive Interference
Destructive Interference Waves with different amplitudes
Standing Waves Result from interference between a wave and its reflected wave. http://www.walter-fendt.de/ph14e/stwaverefl.htm http://id.mind.net/~zona/mstm/physics/waves/standingwaves/understandingswdi a1/understandingswdia1.html
Node Antinode
refraction Destructive interference diffraction reflection
Light & Wave Behaviors Lab
When light passes through a series of tiny slits or grooves called a diffraction grating, light fans out from each slit. White light is spread out into a spectrum according to wavelength.
Refraction Pouring water in the cup causes the light to refract at a different angle. This is why the penny is no longer in view when looking at it from the original viewing angle.
Light waves bounce off the inner and outer layers of the nail polish film. At times the waves interfere constructively to produce certain colors and destructively to produce other colors.
You could see the image of each other when the angles were the same. The law of reflection states that the angle of incidence equals the angle of reflection.
How is amplitude altered during constructive/destructive interference? Constructive interference results a combined wave with a larger amplitude than the separate waves. Destructive interference results in a combined wave with a smaller amplitude than the separate waves. Wave Behaviors Discussion Wave Behaviors lab Lab Explanations
Classify this wave behavior and determine the amplitude if A=2 cm and B=5 cm. Constructive Interference Amplitude = 7 cm Sound Notes and Video Clips Resonance Speed of Sound & Sonic Boom Doppler Effect How are frequency and pitch of a sound wave altered as sound moves away from you?
Sound travels as a longitudinal wave Sound waves are created by vibrations.
FREQUENCY Frequency is known as Pitch in sound waves Human hearing: 20 Hz to 20,000 Hz Infrasonic: <20 Hz Ultrasonic: >20,000 Hz
AMPLITUDE Amplitude is known as Loudness in sound waves Loudness measured in decibels (db) Near total silence 0 db A whisper - 15 db Normal conversation - 60 db A lawnmower - 90 db A car horn - 110 db A rock concert or a jet engine - 120 db A gunshot or firecracker - 140 db
More Sound Terminology Natural Frequency is the frequency at which an object naturally vibrates Resonance occurs when an outside vibration matches the natural frequency of an object causing it to vibrate
VELOCITY The speed of a sound wave depends on: 1. The type of Medium Fastest in solids 2. The Temperature of the medium Faster in warmer temps
Other Scenarios of Doppler Effect Object is traveling at the speed of sound
Other Scenarios of Doppler Effect Object is traveling faster than the speed of sound Creates sonic booms
Pitch and the Doppler Effect
Wavelength and Frequency Review As the wavelength increases, the frequency. decreases This means wavelength and frequency are indirectly proportional. Which of these waves has the higher frequency? This one! It has the smaller wavelength.
Frequency and Sound Frequency = pitch Pitch the highness or lowness of a sound High frequency: high pitch Low frequency: low pitch
DOPPLER EFFECT The perceived change in frequency (pitch) due to the motion of either the source of the wave and/or the observer
How does it happen? As a sound is created, the sound waves spread out in all directions around the source.
If the source moves, the wave becomes bunched up on one side and more spread out on the other. Then What?
Doppler Effect If the sound is moving away from you... If the sound is moving towards you... Lower pitch; longer wavelength Lower frequency Higher pitch; shorter wavelength Higher frequency
So, what does that mean? If the source is moving towards you, the pitch sounds higher. And if the source is moving away from you, the pitch sounds lower.
http://www.youtube.com/watch?v=-d9a2oq1n38 http://www.youtube.com/watch?v=gwglaaydbbc http://www.youtube.com/watch?v=ofesdvdx-fy http://www.youtube.com/watch?v=z0eaoilzgge http://youtu.be/h4onbyrbcjy http://youtu.be/sh7xsx10qkm
Classify this wave behavior and determine the amplitude if A=2 cm and B=5 cm. Constructive Interference Amplitude = 7 cm How are frequency and pitch of a sound wave altered as sound moves away from you? Frequency will decrease as the sound moves away from you causing the pitch to seem lower. Sound Notes and Video Clips Resonance Speed of Sound & Sonic Boom Doppler Effect
REVIEW 1. Review of EM Spectrum 2. Wave Test Review Classify this wave behavior and determine the amplitude if A=2 cm and B=5 cm. Destructive Interference Amplitude = 3 cm Echoes are examples of what wave behavior? Reflections 80
The Electromagnetic Spectrum Question & Answer
Which EM wave has the longest wavelength, thus the lowest amount of energy? Radio
Which EM wave is the only one that can be seen by the human eye? Visible Light
Which EM wave is shorter than radio waves, but longer than infrared? Microwaves
Which EM wave aids in photosynthesis and provides vitamin D to people? Ultraviolet
Which EM wave has the most energy and is the most intense and dangerous? Gamma
Which EM wave is used at the airport to see through suitcases and bags? X-rays
Which EM wave is the heat given off by objects? Infrared
Conclusion Electromagnetic Waves: Can travel in a vacuum Speed of all EM waves is 3.0 x 10 8 m/s in a vacuum Slows down in gas, slower in liquids, slowest in solids
Review BR: Classify this wave behavior. Refraction How is this different from Diffraction? Refraction is the bending of a wave due as it enters a new medium, but diffraction is the bending of a wave around an obstacle or 91 opening.
REVIEW Which wave behavior caused this glass to break? Resonance What are the basic properties of sound? 1. Wave Stations 2. QR Code Questions 96
Sound Lab Summary Pay close attention as we discuss some of the things you say in the lab activities. You will use this information to explain how each activity worked.
Sounds are produced by vibrations. Sound waves are LONGITUDINAL.
Frequency = Pitch The shorter the wavelength, the higher the pitch. Humans can hear between 20 Hertz (infrasonic) and 20,000 Hertz (ultrasonic) http://www.ultrasonic-ringtones.com/
Natural Frequency All objects produce their own unique frequency and sound (timbre)
Resonance When a sound matches the natural frequency of an object causing it to vibrate
Amplitude = Loudness Constructive interference creates louder sounds
Media Sound travels best (and fastest) through solids Sound cannot travel through empty space
1. creates louder sounds. * constructive interference B. destructive interference C. diffraction
2. All objects produce their own unique frequency and sound called. A. resonance B. natural pitch * natural frequency
3. The longer the wavelength the the pitch? A. longer B. higher * lower
4. When a sound matches the natural frequency of an object causing it to vibrate * B. C. resonance natural frequency tone
5. Sound travels best (and fastest) through A. gases * solids C. liquids
6. Sounds less than 20 Hz are A. supersonic B. ultrasonic * infrasonic
REVIEW Which wave behavior caused this glass to break? Resonance What are the basic properties of sound? Sound travels as a longitudinal wave and can experience many different wave behaviors: resonance, constructive/destructive interference, resonance, frequency/amplitude changes. 1. Wave Stations 2. QR Code Questions 110