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