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