A Waves Waves w rhythmic disturbances that carry
A. Waves Ø Waves w rhythmic disturbances that carry energy through matter or space Ø Medium w material through which a wave transfers energy w solid, liquid, gas, or combination w electromagnetic waves don’t need a medium (e. g. visible light)
A. Waves ØTwo Types: Longitudinal Transverse
B. Transverse Waves ØTransverse Waves w medium moves perpendicular to the direction of wave motion
B. Transverse Waves ØWave Anatomy crests wavelength corresponds to the amount of energy carried by the wave amplitude nodes wavelength troughs
C. Longitudinal Waves ØLongitudinal Waves (a. k. a. compressional) w medium moves in the same direction as wave motion
C. Longitudinal Waves ØWave Anatomy compression rarefaction wavelength Amount of compression corresponds to amount of energy AMPLITUDE.
D. Measuring Waves ØFrequency ( f ) w # of waves passing a point in 1 second w Hertz (Hz) w shorter wavelength higher frequency higher energy 1 second
D. Measuring Waves ØVelocity ( v ) w speed of a wave as it moves forward w depends on wave type and medium v= ×f v: velocity (m/s) : wavelength (m) f: frequency (Hz)
D. Measuring Waves Ø EX: Find the velocity of a wave in a wave pool if its wavelength is 3. 2 m and its frequency is 0. 60 Hz. WORK: v= ×f GIVEN: v=? = 3. 2 m f = 0. 60 Hz v = (3. 2 m)(0. 60 Hz) v v = 1. 92 m/s f
D. Measuring Waves Ø EX: An earthquake produces a wave that has a wavelength of 417 m and travels at 5000 m/s. What is its frequency? WORK: f=v÷ GIVEN: = 417 m v = 5000 m/s f=? v f = (5000 m/s) ÷ (417 m) f = 12 Hz f
Ch. 10 - Waves & Sound II. The Nature of Sound Ø Speed of Sound Ø Human hearing Ø Doppler effect Ø Seeing with sound
A. Speed of Sound Ø 344 m/s in air at 20°C ØDepends on: w Type of medium • travels better through liquids and solids • can’t travel through a vacuum w Temperature of medium • travels faster at higher temps
B. Human Hearing sound wave vibrates ear drum amplified by bones converted to nerve impulses in cochlea
B. Human Hearing ØPitch w highness or lowness of a sound w depends on frequency of sound wave w human range: 20 - 20, 000 Hz ultrasonic waves subsonic waves
B. Human Hearing ØIntensity w volume of sound w depends on energy (amplitude) of sound wave w measured in decibels (d. B)
B. Human Hearing DECIBEL SCALE 100 70 40 0 10 18 80 110 120
C. Doppler Effect ØDoppler Effect w change in wave frequency caused by a moving wave source w moving toward you - pitch sounds higher w moving away from you pitch sounds lower
C. Doppler Effect Stationary source same frequency in all directions Moving source Supersonic source lower higher frequency waves combine to produce a shock wave called a sonic boom
D. Seeing with Sound ØUltrasonic waves - above 20, 000 Hz Medical Imaging SONAR “Sound Navigation Ranging”
Ch. 11 - Waves & Sound III. Music Ø Music vs. Noise Ø Resonance Ø Harmonics Ø Interference Ø Acoustics
A. Music vs. Noise ØMusic w specific pitches and sound quality w regular pattern ØNoise w no definite pitch w no set pattern
B. Resonance ØForced Vibration w when one vibrating object forces another object to vibrate at the same frequency w results in a louder sound because a greater surface area is vibrating w used in guitars, pianos, etc.
B. Resonance ØResonance w special case of forced vibration w object is induced to vibrate at its natural frequency
B. Resonance “Galloping Gertie” The Tacoma Narrows Bridge Disaster Wind through a narrow waterway caused the bridge to vibrate until it reached its natural frequency.
C. Harmonics ØFundamental w the lowest natural frequency of an object ØOvertones w multiples of the fundamental frequency
D. Interference ØInterference w the ability of 2 or more waves to combine to form a new wave Constructive - louder Destructive - softer
D. Interference ØBeats w variations in sound intensity produced by 2 slightly different frequencies w both constructive and destructive interference occur
E. Acoustics ØAcoustics w the study of sound ØReverberation w echo effect produced by the reflection of sound Anechoic chamber - designed to eliminate reverberation.
Ch. 11 - Light III. Wave Properties of Light Ø Reflection Ø Refraction Ø Diffraction Ø Interference
A. Reflection Normal ØReflection w when a wave strikes an object and bounces off incident beam reflected beam
A. Reflection ØLaw of Reflection w the angle of incidence equals the angle of reflection
B. Refraction ØRefraction w bending of waves when passing from one medium to another w caused by a change in speed • slower (more dense) light bends toward the normal • faster (less dense) light bends away from the normal SLOWER FASTER
B. Refraction ØRefraction depends on… w speed of light in the medium w wavelength of the light - shorter wavelengths (blue) bend more
B. Refraction ØExample: View explanation.
C. Diffraction ØDiffraction w bending of waves around a barrier w longer wavelengths (red) bend more opposite of refraction
D. Interference ØInterference w constructive brighter light w destructive dimmer light
E. Cool Applications! ØFiber Optics w Total Internal Reflection • when all light is reflected back into the denser medium
E. Cool Applications! ØThe “Broken Pencil” w refraction View animation and explanation of the “Broken Pencil. ”
E. Cool Applications! ØRainbows w refraction-reflection-refraction
E. Cool Applications! ØDiffraction Gratings w glass or plastic made up of many tiny parallel slits w may also be reflective w spectroscopes, reflective rainbow stickers, CD surfaces
E. Cool Applications! ØThin Films - Bubbles & Oil Slicks w interference results from double reflection
E. Cool Applications! ØBlue Sky & Red Sunsets • Molecules in atmosphere scatter light rays. • Shorter wavelengths (blue, violet) are scattered more easily. SUNSET • more atmosphere • more scattering • orange-red sky & sun NOON • less atmosphere • less scattering • blue sky, yellow sun
Ch. 11 - Light II. Light and Color Ø Light and Matter Ø Seeing Colors Ø Mixing Colors
A. Light and Matter ØOpaque w absorbs or reflects all light ØTransparent w allows light to pass through completely ØTranslucent w allows some light to pass through
B. Seeing Colors ØWhite light w contains all visible colors - ROY G. BIV ØIn white light, an object… w reflects the color you see w absorbs all other colors REFLECTS ALL COLORS ABSORBS ALL COLORS
B. Seeing Colors Stimulates red & green cones ØThe retina contains… w Rods - dim light, black & white w Cones - color • red - absorb red & yellow • green - absorb yellow & green • blue - absorb blue & violet Stimulates all cones
B. Seeing Colors ØColor Blindness w one or more sets of cones does not function properly Test for red-green color blindness.
C. Mixing Colors ØPrimary light colors w red, green, blue w additive colors w combine to form white light w EX: computer RGBs View Java Applet on primary light colors.
C. Mixing Colors ØFilter w transparent material that absorbs all light colors except the filter color View Java Applet on filters.
C. Mixing Colors ØPigment w colored material that absorbs and reflects different colors ØPrimary pigment colors w cyan, magenta, yellow w subtractive colors w combine to form black w EX: color ink cartridges
C. Mixing Colors Light Pigment When mixing pigments, the color of the mixture is the color of light that both pigments reflect.
Negative Afterimage - One set of cones gets tired, and the remaining cones produce an image in the complimentary color.
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