Post on 16-May-2015
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Today: Electromagnetic Radiation; Light & Sources of Light; Atomic spectra
Steve Block Lab, Stanford
Optical tweezers study of RNA polymerase
Exam 1 Results
Electromagnetic radiation / wave
Carries energyHas momentum (oomph) (but does NOT have mass)In a vacuum travels at “light speed” (duh?)Behaves like particle AND wave (what the???)Oscillating Electric and Magnetic “Field”
Electromagnetic spectrum
Wavelength(meters)
Frequency(Hz)
Temperaturerequired to glow
this color
Carries energyHas momentum (oomph) (but does NOT have mass)In a vacuum travels at “light speed” (duh?)Behaves like particle AND wave (what the???)Oscillating Electric and Magnetic “Field”
Electromagnetic radiation / wave
Wavelength(meters)
Frequency(Hz)
Temperaturerequired to glow
this color
More like waves More like particles
Clicker Question—Electromagnetic Waves, Frequency
Which of these EM waves has the highest frequency
A. RadiowaveB. UltravioletC. Visible red lightD. Microwave
Clicker Question—Electromagnetic Waves, Frequency
Which of these EM waves has the highest frequency
A. RadiowaveB. UltravioletC. Visible red lightD. Microwave
What are sources of electromagnetic radiation (EM)?
Sunshine … fusion / atoms?Core of Earth (Earth’s magnetism)Microwave (oven/sure) …. ElectronsCell phones (microwaves) … electrons are oscillatingRadio waves … antennaes … metal electricity / electronsGamma rays … from pulsars (could be proton / neutrons)Infrared and light waves from an explosion (lots of different electron thing)
You are always basking in a glow of EM radiation!
EM Waves are everywhere, alwaysEven in the “dark” or in “space”
Because you are at 310 Kelvin (98.6 degrees),you emit radiation yourself!
Cosmic Background Microwave Radiation
Universe Opaque
Universe Transparent
Visible light is a small portion of the EM spectrumBut of course, the most “colorful”!
Key concept: Energy of photon is proportional to frequencyE = h * f
Models of the atom evolved quickly in the early 1900’s
Plum Pudding“Solar System” model
Electron “Shells”Figure 11.6 in texbook
http://www.csmate.colostate.edu/cltw/cohortpages/viney/atom2.jpg
Electron cloudshttp://www.youtube.com/watch?v=fKYso97eJs4&feature=related
Atomic spectra
http://www.walter-fendt.de/ph11e/bohrh.htm(Standing waves and resonance for Bohr model)
http://www.lon-capa.org/~mmp/kap29/Bohr/app.htm
http://www.youtube.com/watch?v=l4yg4HTm3ukSpectrum of the stars
A) Each type of gas has a different molecular weight, which causes the nucleus to have different possible energy levels
B) Each type of gas has a different orbital structure, which leads to different possible electron energy differences in the emission lines
What causes the emission lines of various gases to differ in color?
Laser light can be used to create a real-life “tractor beam”
Fictional Tractor Beam
Steve Block Lab, Stanford
“Laser Tweezers” for biophysics experiments
Microsphere
Biomolecular“Tether”
Coverglass
Dig-Antidig
Biotin-streptavidin
“Laser Tweezers” or “Optical tweezers” have become incredibly powerful tools for biophysics
Optical tweezers I built at Cornell(M. Wang lab w/ Richard Yeh)
Here are some actual videos of optical tweezers in action
Sorting colored microsphereshttp://www.ppo.dk/Research-OT.html
Fiber optical trap, http://members.yline.com/~tweezers/gallery.htm
Kinesin Molecular Motorhttp://www.scripps.edu/milligan/research/movies/kinesin_mpg.html
Steve Block Lab, Stanford
Clicker Question—Light
Hopefully you know that light carries energy. But does light carry momentum?
A. Yes, alwaysB. SometimesC. No! Light does NOT have mass!
Edned lecture here