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Physical Science CHAPTER 23 Waves

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Waves transmit energy!!! Mechanical Vs. Electromagnetic Waves

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Mechanical Waves Need medium (gas, liquid, solid) Examples: Sound, water waves

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Electromagnetic Waves No medium needed. Example: Visible Light (ROYGBIV), Ultraviolet, Infrared, Microwaves, etc…

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http://www.lbl.gov/MicroWorlds/ALSTool/EMSpec/EMSpec2.html

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3 main characteristics of all Waves 1. Amplitude (high amplitude means high energy) 2. Wavelength (Unit: meters) 3. Frequency Units: cycles/sec Waves/sec 1/s Hertz (Hz)

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Frequency Example Problem 1.A boy standing on a dock counts 20 waves pass by in 5 seconds. What is the frequency of the waves? f = #waves / time 20 waves / 5 seconds = 4 Hz

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Frequency Example Problem #2 2.If the frequency of the waves is increased to 8 Hz, how many waves will pass by the boy in 2 seconds? f = #waves / time 8 Hz = #waves / 2 seconds 8 Hz x 2 seconds = 16 waves

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MECHANICAL WAVES (2 TYPES) TRANSVERSE WAVES LONGITUDINAL WAVES

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SURFACE WAVES http://www.gmi.edu/~drussell/Demos/waves/wavemotion.html

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TRANSVERSE WAVE

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LONGITUDINAL WAVE

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SPEED OF WAVES speed = frequency x wavelength v = f x λ Example #1 A wave on a lake is traveling with a velocity of 8 m/s. the frequency is 2 Hz. What is the wavelength of this wave? 8 m/s = 2 Hz x λ λ = 4 m

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The Type Of Medium Determines the Speed of The WAVE!! Higher Density = Slower Speed of Wave Higher Elasticity = Faster Speed of Wave

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THE 4 BASIC WAVE INTERACTIONS ARE: 1. REFLECTION 2. REFRACTION 3. DIFFRACTION 4. INTERFERENCE

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1. REFLECTION Bouncing back of waves upon reaching another surface.

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THE LAW OF REFLECTION STATES THAT THE ANGLE OF INCIDENCE IS EQUAL TO THE ANGLE OF REFLECTION.

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2. REFRACTION Bending of waves due to a change in speed.

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3. DIFFRACTION Bending of waves around the edge of an obstacle.

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4. INTERFERENCE 1. CONSTRUCTIVE INTERFERENCE When waves combine and produce a wave that is greater than either of the waves alone.

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2. DESTRUCTIVE INTERFERENCE When waves combine and produce a wave that is less than either wave alone.

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Applet Interference by 3 waves simultaneously. http://www.chipr.sunysb.edu/eserc/ProjectJava/WaveInteractionApplet/ Another wave website to look at: http://www.howe.k12.ok.us/~jimaskew/pwave.htm

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STANDING WAVES RESONANT FREQUENCY (or natural frequency) The frequency at which a standing wave occurs.

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RESONANCE The ability of an object to vibrate by absorbing energy of its own natural frequency. Video clip of the Tacoma Narrows Bridge November 1940 http://www.gmi.edu/~drussell/Demos.html http://www.gmi.edu/~drussell/Demos.html

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NODES Stationary points of a standing wave. ANTINODES Loops of a standing wave where maximum oscillation of the medium occurs.

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