A1 03 EM Radiation
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Transcript of A1 03 EM Radiation
Electromagnetic RadiationLACC §4.2, 4.3, 4.5
• Electromagnetic (EM) Radiation as a wave
• Electromagnetic (EM) Radiation as a particle
• Interactions between EM Radiation (e.g. light) and Matter
All we know about objects beyond our solar system comes (almost) solely from examining
the radiation (e.g. light) they emit.
1Wednesday, February 17, 2010
Electromagnetic Radiationis a wave
• EM radiation is pure energy (it has no mass)
• EM radiation results from the motion of charged objects
• EM radiation travels at the speed of light through a vacuum (and at lesser speeds through matter)
• EM radiation is completely described by its frequency, intensity, and direction of travel.
2Wednesday, February 17, 2010
Waves: Diffraction
http://www.gcsescience.com/pwav37.htm
If the wavelength is of a similar size to a gap ...
then the wave will diffract as shown
below.
If the wavelength does not match the size of
the gap, then only a little diffraction will occur at the edge of the wave.
3Wednesday, February 17, 2010
Waves: Interference
http://www.twow.net/ObjText/OtkCaLdQmB.htm
4Wednesday, February 17, 2010
Waves: Interference
http://www1.union.edu/newmanj/lasers/Light%20as%20a%20Wave/light_as_a_wave.htm
The diffraction pattern of light observed on a distant screen when a He-Ne beam passes
through a single narrow slit;
The same when the beam passes through two identical closely
spaced slits.
5Wednesday, February 17, 2010
EM Radiation as a Wave
http://www.bbemg.ulg.ac.be/UK/2Basis/freqlength.html
v = fλv = velocityf = frequencyλ = wavelength
Q: What is v for light?A: c, the speed of light = 3x108 m/s = 186,400 miles/s
6Wednesday, February 17, 2010
E.g. Light
http://www.uark.edu/ua/pirelli/html/color_freq_wavelength.html
7Wednesday, February 17, 2010
• atoms and molecules absorb and emit photons
• a photon is a single packet of EM energy
Electromagnetic Radiationis a particle
8Wednesday, February 17, 2010
Atoms Emit Photons
http://www.astrosociety.org/education/publications/tnl/35/light3.html
E = hf
E = energyh = Plank’s constantf = frequency
h = 6.626x10-34 J•sThis makes Plank’s constant the smallest(?) constant in physics.
9Wednesday, February 17, 2010
Atoms Absorb and Emit Individual Photons
http://steve.files.wordpress.com/2006/03/Absorption%20emission.jpg
10Wednesday, February 17, 2010
The EM Spectrum
http://www.nhn.ou.edu/~jeffery/course/c_energy/energyl/lec001.html
• Credit: Philip Ronan who has given permission to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version.
• Download site: Wikipedia: Image:EM spectrum.svg.
11Wednesday, February 17, 2010
EM Radiation:Wave or Particle?
Waves
• interactions between waves results in interference patters
• radiate out from a source
• can bend around corners
• can bend around obstacles
Particles
• interactions between particles result in collisions
• are “shot” out in specific directions
• travel in straight lines
• are blocked by obstacles
12Wednesday, February 17, 2010
Electromagnetic RadiationLACC §4.2, 4.3, 4.5
• Electromagnetic (EM) Radiation as a wave (v = fλ)
• Electromagnetic (EM) Radiation as a particle (i.e. photons, E=hf)
• Interactions between EM Radiation (e.g. light) and Matter: absorption/emission of EM radiation by atoms/molecules
All we know about objects beyond our solar system comes (almost) solely from examining
the radiation (e.g. light) they emit.
13Wednesday, February 17, 2010
LACC HW: Franknoi, Morrison, and Wolff, Voyages Through the Universe,
3rd ed.
• Ch. 4, pp. 106-107: 11. Choose your answers from: radio | microwave | infrared | visible | ultraviolet | X-ray | gamma ray.
Due at the beginning of next week’s first class.
14Wednesday, February 17, 2010
SpectroscopyLACC §4.2, 4.3, 4.5
• Thermal Spectra: Wien’s Law, Stefan-Boltaman Law
• Types of Spectra: there are 3 types of spectra
• Spectroscopy: what can it tell us?
All we know about objects beyond our solar system comes (almost) solely from examining the
electromagnetic radiation (e.g. light) they emit.
15Wednesday, February 17, 2010
Thermal Radiation
http://cse.ssl.berkeley.edu/bmendez/ay10/2002/notes/pics/bt2lf0612_a.jpg
http://astro.unl.edu/classaction/animations/light/meltednail.htmlBlackbody Curves or Melting
http://astro.unl.edu/classaction/animations/light/bbexplorer.htmlBlackbody Curves (NAAP)
16Wednesday, February 17, 2010
Thermal Radiation
http://feps.as.arizona.edu/outreach/bbwein.html
T = Temperatureλ = peak wavelength
Wein’s law
17Wednesday, February 17, 2010
Thermal Radiation
http://csep10.phys.utk.edu/astr162/lect/light/radiation.html
F = σT4
F = energy fluxσ = Stefan-Boltzmann
constantT = temperature
Stefan-Boltzmann law
18Wednesday, February 17, 2010
Types of Observed Spectra
http://instruct1.cit.cornell.edu/courses/astro101/lectures/images/lec07_04.jpg
http://astro.unl.edu/classaction/animations/light/threeviewsspectra.htmlThree Views Spectrum Demonstrator
19Wednesday, February 17, 2010
Atomic Energy Levelsof Hydrogen
http://www.daviddarling.info/encyclopedia/H/
hydrogen_spectrum.html
http://astro.unl.edu/classaction/animations/light/hydrogenatom.htmlBlackbody Curves (NAAP)Hydrogen Atom Simulator (NAAP)
20Wednesday, February 17, 2010
EM Rad. & Space--Our Sun
http://www.weasner.com/etx/guests/2004/guests_spectra.html
21Wednesday, February 17, 2010
http://mais-ccd-spectroscopy.com/Planetary%20Nebula.htm
EM Rad. & Space--Orion N.
22Wednesday, February 17, 2010
EM Rad. & Space--M.W.
23Wednesday, February 17, 2010
Images vs. Spectra
Which is better, the image of an astronomical object, or the spectrum of an astronomical object?
What about photometry?
24Wednesday, February 17, 2010
SpectroscopyLACC §4.2, 4.3, 4.5
• Types of Spectra: Continuous, Emission Line, Absorption Line
• Thermal (or Blackbody) Spectra: Wien’s Law (Temperature), Stefan-Boltaman Law (Power)
• Spectroscopy: Temperature, Composition, Doppler Shift, Density
All we know about objects beyond our solar system comes (almost) solely from examining the
electromagnetic radiation (e.g. light) they emit.
25Wednesday, February 17, 2010
LACC HW: Franknoi, Morrison, and Wolff, Voyages Through the Universe,
3rd ed.
• Ch. 4, pp. 106-107: 23, 24.
• Ch 5: Tutorial Quizzes accessible from: http://www.brookscole.com/cgi-brookscole/course_products_bc.pl?fid=M20b&product_isbn_issn=9780495017899&discipline_number=19
Due at the beginning of next class period.
26Wednesday, February 17, 2010