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Waves, Light, & Sound Chapter 6
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Student Learning Objectives Analyze wave motion Recall attributes of electromagnetic waves & sound waves Explain resonance
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What are the basic properties of waves? A wave is a traveling disturbance that carries energy from place to place.
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Practice When a ship that is 100 feet from a sailboat passes the sailboat, does the water travel with the wave from the ship to the sailboat? 100 feet
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All waves begin as a vibration! When something moves back and forth repeatedly, this is vibration.
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There are two basic types of waves. Transverse (perpendicular vibration) Longitudinal (parallel vibration)
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What do you think the vibrational motion is for a water wave?
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Wave Properties Wavelength (distance/one cycle) Period (time for one cycle) Frequency (cycles per second) f =1 T
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Wave speed (distance per time) Amplitude (displacement/energy) The wavelength or frequency determines the sound we hear or the type of “light” we see. v = f c = f
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Practice While sailing on the ocean, you notice waves cresting 2 feet above the level horizon. These waves are hitting your boat every 1.5 seconds. As you look out over the water, you estimate the distance between crests to be 5 meters. Analyze this wave and determine wavelength, period, frequency, speed, & amplitude
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What is an electromagnetic wave? Electromagnetic radiation is a self-propagating wave. Changing E Field Changing B Field self-propagating
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http://www.chromoscope.net/
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Light Speed All electromagnetic waves travel at the same speed in a vacuum (in space). In metricsIn miles 3 x 10 8 m/s186,000 miles/sec 3 x 10 5 km/s670 x 10 6 mph
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The energy we are now observing from objects in space was generated in the past. Sun8 min. Proxima Centauri4.2 LY Sirius8.6 LY Andromeda Galaxy2.5 x 10 6 LY
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Practice 1) A particular ray of red light has a frequency of 4.2 x 10 14 Hz. What is the wavelength of this red light? 2) Predict which would have a longer wavelength, radio waves broadcast at 95.1 MHz or radio waves broadcast at 1220 MHz. Calculate the wavelength of each of these waves to test your prediction.
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Colors We interpret particular wavelengths of visible light as particular colors. ROY G BVROY G BV
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Each color of the visible spectrum corresponds to a specific wavelength, frequency, energy, & temperature. RedYellowBlue 650 nm575 nm475 nm Low EnergyHigh Energy CoolHot
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The primary source of infrared radiation is heat or thermal radiation. A particle of electromagnetic radiation is called a photon. http://spaceplace.nasa.gov/ir-photo-album/en/
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What are the basic attributes of a sound wave? A sound wave is a longitudinal wave traveling through matter. Vibrations cause compressions and rarefactions Molecules vibrate “side-to-side” (molecules collide) In metricsIn miles 343 m/s770 mph
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Practice 1) If you see lightening and then hear the thunder 3 seconds later, how far away is the storm? 2) In a science fiction movie, when a spaceship explodes, we see and hear the explosion at the same time. What is wrong with this scenario?
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Pitch is an interpretation of sound frequency. http://www.freemosquitoringtones.org/hearing_test/ Humans20-20,000 Hz Dog67-45,000 Hz Cat45-64,000 Hz Guinea Pig54-50,000 Hz Bat2,000-110,000 Hz Goldfish20-3,000 Hz
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Too Loud! Decibels measure the intensity of sound, or the loudness. 85+ can damage human ears 120+ can rupture the ear Whisper20 dB Conversational Speech60 dB Biodegradable Sun Chip Bag95 dB Artillery Fire140 dB
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Ultrasound An echo is a reflected wave. Ultrasound (f = 20,000 Hz +) Reverberations are the mixing of multiple reflected waves. Louder Volume/Random Mixing
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Refraction ( v) of sound wave occurs when density changes. Bending http://www.schoolphysics.co.uk/age16- 19/Sound/text/Refraction_of_sound/index.html
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Why does the sound of a train whistle change? When there is relative motion between a wave source and an observer, wavelengths are altered. Doppler Effect
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Object moving towards observer, the wave is blue shifted. shortened f increased (higher pitch) Object moving away from observer, the wave is red shifted. lengthened f decreased (lower pitch)
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Doppler Effect
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What is a sonic boom? A sonic boom is caused by a large change in pressure. No Speed Mach 1 Mach 2
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The compression waves in a fluid stack up when an object travels at the speed of the waves or faster. (Shock Wave ) Stacked compression spheres Sonic boom
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Practice 1) Why don’t we hear a sonic boom every time a jet passes overhead? (3 possibilities) 2) Why are there two booms in a sonic boom?
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What happens when waves interfere with each other? Vibrational amplitudes add together. Increase in Amplitude Vibrational amplitudes cancel each other. Decrease in Amplitude
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Practice 1)What is an example of constructive interference? 2)What is an example of completely destructive interference?
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Sound waves that are out slightly of phase result in beats.
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Standing Waves A wave and its reflection can add to produce a standing wave.
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Resonance Each material has its own natural frequency of vibration. Resonance occurs when incoming wave vibrations match an object’s natural frequency. Tacoma Narrows Bridge Collapse (1940)
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Incoming energy is transferred Vibrational energy increases Amplitude increases Resonance
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Examples of ResonanceBOOM Music
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