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Light & SoundBRHS- Physics
2012
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Electromagnetic Radiation
Energy that has properties of both particles and waves
Particles – have mass and occupy space
Waves – no mass but carry energy
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Electromagnetic Radiation – www.google.images
http://www.ndt-ed.org/EducationResources/CommunityCollege/RadiationSafety/theory/nature.htm
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Wave propertiesAmplitude – the height of the waves
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Wave propertiesFrequency () – the number of waves that pass a
given point per unit of time units of hertz (Hz or s –1)
Low
High
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Wave properties• Wavelength () – the distance between a crest and
a crest or a trough and a trough in m or nm
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Relationship of frequency and wavelength
Frequency x wavelength = speed
= c (speed of light)
c = 2.998 x 108 m/s
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1. Lasers used with DVD players have a wavelength of 650 nm. What is the frequency of this light in hertz (Hz)?
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2. Calculate the frequency of yellow light that has a wavelength of 584 nm.
3. Calculate the wavelength in nm of violet light having a frequency of 7.32 x 1014 Hz.
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Electromagnetic Radiation Figure 7.10
General Chemistry, 4th Ed., Hill, Petrucci, McCreary and Perry
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Electromagnetic Radiation Fig 3.3
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Continuous Spectra
White light passed through a prism produces a spectrum – colors in continuous form.
~ 650 nm ~ 575 nm
~ 500 nm
~ 480 nm
~ 450 nm
The different colors of light correspond to different wavelengths and frequencies
Fig 7.11 General Chemistry, 4th Ed., Hill, Petrucci, McCreary and Perry
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Line SpectraFig 7.12 General Chemistry, 4th Ed., Hill, Petrucci, McCreary and Perry
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Line Spectra
The pattern of lines emitted by excited atoms of an element is unique = atomic emission spectrum
Fig 7.13 General Chemistry, 4th Ed., Hill, Petrucci, McCreary and Perry
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Fig 7.17 General Chemistry, 4th Ed., Hill, Petrucci, McCreary and Perry
ΔElevel= h
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Demonstration with light itemshttp://www.hsphys.com/light_and_optics.ht
ml
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1905 Albert Einstein – photons energy packets explained the photoelectric effect
E = hh = 6.626 x 10–34 joules (J)
Planck’s constant
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Fig 7.15 General Chemistry, 4th Ed., Hill, Petrucci, McCreary and Perry
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http://arts.ucsc.edu/EMS/music/tech_background/TE-01/teces_01.html
Sound moves in waves through a medium (air) having a random arrangement of molecules in a constant rate that is recognized by the ear
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http://arts.ucsc.edu/EMS/music/tech_background/TE-01/teces_01.html
If sound hits a soft surface, the wave moves around the object, but if it hits a rigid surface,
1. a wave is set up within the material and is a function of the composition of the material
2. rest of the energy is reflected in waves like light off a mirror as a function of distance
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http://arts.ucsc.edu/EMS/music/tech_background/TE-01/teces_01.html
If sound hits a surface with a small hole, the wave moves through the hole in waves,
If 2 or more holes are present, diffraction occurs
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http://arts.ucsc.edu/EMS/music/tech_background/TE-01/teces_01.html
diffraction when waves
add (reinforce or constructive interference) or
subtract (nulls or destructive interference)
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constructive interference – sound gets louder
destructive interference – sound gets softer
Sound effects easily observed by the ear
http://www.mrfizzix.com/instruments/basics.html
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http://www.mrfizzix.com/instruments/basics.html
Intensity = Energy
Time x Area
Intensity = Power
Area
OR
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Sound Ranges
www.physics.ubc.ca/~outreach/phys420/p420_03/.../overheads.doc
Humans can hear sounds between 20Hz- 20000Hz
Ultrasonic waves are waves above 20000Hz; Infrasonic waves are waves below 20Hz
Most bat and dog communication is ultrasonic while elephants and whales are infrasonic
http://www.youtube.com/watch?v=iWfjcdOcwRs&safety_mode=true&persist_safety_mode=1&safe=active
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Pitch How the brain interprets the frequency of an emitted sound.
higher the frequency, the higher the pitch.
lower the frequency, the lower the pitch
www.physics.ubc.ca/~outreach/phys420/p420_03/.../overheads.doc
Frequency is in 1 Hertz = 1 vibration/sec
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tonie3c.blogspot.com
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www.healthinformation.nhs.uk
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scienceblogs.com
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Demonstration with tuning forks
Smaller forks have higher pitch
Larger forks have lower pitch
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Demonstration with Physics of Music
Experiencing pitch
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Doppler EffectChristian Doppler (1805-1853): An Austrian
physicist who conducted experiments with musicians on railway trains playing instruments as the train approached them and receded from them.
www.physics.ubc.ca/~outreach/phys420/p420_03/.../overheads.doc
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Doppler Effect
The Doppler Effect is a change in pitch, due to the relative motion between a source of sound and the receiver.
common example: change in pitch as a car horn or siren on a vehicle moves past us
www.physics.ubc.ca/~outreach/phys420/p420_03/.../overheads.doc
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www.physics.ubc.ca/~outreach/phys420/p420_03/.../overheads.doc
Doppler Effect Illustrated
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http://boomeria.org/physicslectures/secondsemester/light/astronomy/doppler.jpg
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http://cse.ssl.berkeley.edu/bmendez/ay10/2002/notes/pics/bt2lf0615_a.jpg
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Doppler Effect ApplicationsRadar Gun
Measure the speed at which a pitcher throwsCatch speederTrack the motion of precipitation caused by storm cloudsUltrasoundMeasure the rate of blood flow in the arteries or the heart.Light“Red-shift”-calculate galaxy speeds
As other galaxies move away from us, the light has a lower frequency than if it were at rest.