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Light & SoundBRHS- Physics
2012
Electromagnetic Radiation
Energy that has properties of both particles and waves
Particles – have mass and occupy space
Waves – no mass but carry energy
Electromagnetic Radiation – www.google.images
http://www.ndt-ed.org/EducationResources/CommunityCollege/RadiationSafety/theory/nature.htm
Wave propertiesAmplitude – the height of the waves
Wave propertiesFrequency () – the number of waves that pass a
given point per unit of time units of hertz (Hz or s –1)
Low
High
Wave properties• Wavelength () – the distance between a crest and
a crest or a trough and a trough in m or nm
Relationship of frequency and wavelength
Frequency x wavelength = speed
= c (speed of light)
c = 2.998 x 108 m/s
1. Lasers used with DVD players have a wavelength of 650 nm. What is the frequency of this light in hertz (Hz)?
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.
Electromagnetic Radiation Figure 7.10
General Chemistry, 4th Ed., Hill, Petrucci, McCreary and Perry
Electromagnetic Radiation Fig 3.3
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
Line SpectraFig 7.12 General Chemistry, 4th Ed., Hill, Petrucci, McCreary and Perry
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
Fig 7.17 General Chemistry, 4th Ed., Hill, Petrucci, McCreary and Perry
ΔElevel= h
Demonstration with light itemshttp://www.hsphys.com/light_and_optics.ht
ml
1905 Albert Einstein – photons energy packets explained the photoelectric effect
E = hh = 6.626 x 10–34 joules (J)
Planck’s constant
Fig 7.15 General Chemistry, 4th Ed., Hill, Petrucci, McCreary and Perry
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
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
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
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)
constructive interference – sound gets louder
destructive interference – sound gets softer
Sound effects easily observed by the ear
http://www.mrfizzix.com/instruments/basics.html
http://www.mrfizzix.com/instruments/basics.html
Intensity = Energy
Time x Area
Intensity = Power
Area
OR
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
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
tonie3c.blogspot.com
www.healthinformation.nhs.uk
scienceblogs.com
Demonstration with tuning forks
Smaller forks have higher pitch
Larger forks have lower pitch
Demonstration with Physics of Music
Experiencing pitch
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
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
www.physics.ubc.ca/~outreach/phys420/p420_03/.../overheads.doc
Doppler Effect Illustrated
http://boomeria.org/physicslectures/secondsemester/light/astronomy/doppler.jpg
http://cse.ssl.berkeley.edu/bmendez/ay10/2002/notes/pics/bt2lf0615_a.jpg
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.