Sound and Light CHAPTER 15. All sound waves Are caused by vibrations.
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Transcript of Sound and Light CHAPTER 15. All sound waves Are caused by vibrations.
Sound and Light
CHAPTER 15
All sound waves
Are caused by vibrations
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All sound waves:
Are longitudinal waves
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All sound waves:
Require a medium -- solid, liquid, or gas.
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The speed of sound
Depends on the medium and temperature
Fastest in most solids
(except ones like rubber that DAMPEN or weaken the sound waves -- these make good soundproofing materials)
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The speed of sound is
Slowest in gases
The colder the gas, the slower the speed
Speed of sound in room temperature air: 346 m/s (760 mi/hour)
Why does sound travel fastest in solids?
The molecules are closer together than in a liquid or gas so they pass on the vibrations more quickly
Loudness of sound depends on wave intensity
Intensity in turn is determined by the amplitude and distance from the source of the sound.
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Intensity
Increases when amplitude increases
Decreases when amplitude decreases
Intensity increases as distance from source decreases
Louder when closer because waves have spread out less
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Loudness is measured in decibels
Logarithmic scale --
70 decibels is twice
as loud as 60
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Frequency determines pitch.
Higher frequency = higher pitchLower frequency = lower pitch
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Beat Frequencies
Interference of two or more frequencies to form a new wave
Frequencies must be close to one another but not the same
Doppler effect
Frequency (and pitch) go up when source of sound is approaching because wavelength is shortened
Go down when source is retreating
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Resonance
Tendency of an object to vibrate with larger and larger amplitudes
ExamplesOpera singer breaking a glassPushing a kid on a swingRunning fingers on rim of a glass
Sonar
Measures distance by measuring time for sound wave to reflect off a surface, calculated distance using d = v x t
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Range of human hearing
20Hz to 20,000 Hz
Ultrasound = Frequency too high for us to hear
Can be used in sonar systemsAbove 20,000 Hz
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Infrasound
Frequencies that are too low to be heard by humans
Below 20 HzExamples:
EarthquakesTornadoesStorms at sea
Light
Sometimes acts
like a waveSometimes acts
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Light acts like a wave when it:Reflects
Refracts
Produces interference
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Light acts like a particle when it:Travels without a mediumDelivers packets of energy (photons) to
solar collectors or chlorophyll
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The energy of light
Is proportional to its frequencyGamma rays have the most energy
because they have the highest frequency.
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The speed of light
Depends on the mediumIn a vacuum, the speed = 3 X 108 m/s.
This speed is known as c
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Light’s brightness depends on wave intensity.
Wave intensity decreases when amplitude decreases
Increases when amplitude increases
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Intensity increases as distance from source decreases
brighter when closer because waves have spread out less
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Electromagnetic spectrum
Light at all possible energies, frequencies, and wavelengths
Entire spectrum given off by sun and other stars
Electromagnetic spectrum
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Radio waves
Longest wavelength, least energyUsed in communication and radar
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microwaves
Next longest wavesUsed in cooking, communication
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Infrared waves
Thermal energy -- heat
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Visible light
Red is longest wavelength of visible light
Violet is shortest
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Ultraviolet (UV) light
9% of sun’s energyCan cause sunburn,
cancerMore dangerous than
visible light because it has a shorter
wavelength
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X-rays
Shorter wavelength than UV light, so more dangerous
Used in medicine, but can disrupt DNA so must limit exposure
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Gamma raysShortest
wavelengths, so most energy (and most dangerous)
Rays can be focused to kill cancer
Given off by radioactive materials
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Reflection
Light bouncing off a surface
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Rough surfaces scatter the light they reflect
so they look dull, not shiny.
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Smooth surfaces reflect the light in the same direction
so they are shiny and can reflect an image.
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Polarization
Filtering of light
Curved mirrors distort images, because different parts of the mirror reflect the light in different directions.
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Objects have the color of the wavelength they reflect.
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Fiber optics use internal reflection to
transmit light along the length of the fibers.
This is more efficient than transmission through metal wires.
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Refraction of Light
Light waves can bend (refract) when they pass from one medium into another.
The waves bend because the new medium changes the waves’ speed.
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Refraction of light
The bending of light waves changes the apparent position of objects.
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Because lenses diffract light, they can:
magnify images (microscope, magnifying glass)
focus images (eye, telescope).
Correct the poor focus of a near- or far- sighted eye (glasses).
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Prisms separate light into its component colors.
This happens because the different colors travel at different speeds and therefore bend different amounts. (Red is fastest and bends the least, so it appears at the top of a rainbow.)
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In rainbows, water droplet act as prisms.
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