A B The Speed of Light Galileo’s Experiment c = Round Trip Distance/Total Time
Jupiter Earth Ole Roemer (1675)
Speed of Light • From Roemer’s Experiment • c = Diameter of Orbit/Time Delay • Modern Value • c = 299,792.458 km/sec
Speed of Light • Absolute constant • Nothing travels faster
Relative Velocities • Our physical sense of velocities is relative • How we measure speed depends on how we are moving and how the object we are measuring in moving Vrel = 2v v v v Vrel = 0 v
Try it with Light Sun ½ c c Intuition says you get ½ c Einstein says c
Try it with Light Sun ½ c c Intuition says you get 1½ c Einstein says c
Nature of Light • Particle? • Newton • Wave? • Christian Huygens in Newton’s day • Thomas Young (1801) • Light can diffract - must be a wave • Transverse wave
Types of Waves • Transverse and Longitudinal
Electromagnetic Spectrum Increasing Wavelength Visible Light
400nm 500nm 600nm 700nm The Visible Spectrum Wavelength means COLOR
Frequency • Number of complete events occurring in a period of time • Waves/second • Examples • Second hand on a clock? • 1 cycle/minute = 1/60 cycle/sec • US Presidential Electons • 1 election/4 years = 1/4 election/year
1 Period = Frequency Frequency and Period
Speed, Wavelength, Frequency c = f
Photon Energy E f E = hf
Properties of Light Speed (c) Nothing travels faster Absolute constant Wavelength () Gamma rays, X-rays, UV, Visible, IR, Radio In visible wavelength means color Frequency (f) Number of complete waves per second Energy of a Photon (E) E = hf
Collimating Lens Imaging Lens Dispersive Element Slit Recording Device Basic Spectrograph
Mercury near Horizon The atmosphere can act like a prism
Continuous Spectrum Source must be HOT and DENSE
Emisson (Bright Line) Spectrum Source must beHOTandTENUOUS
Continuous Emission Absorption Types of Spectra
He “bullet” Atom Rutherford Scattering Experiments
Hydrogen Atoms • Simplest atom • One proton, one electron • Most abundant atom • 90% of universe is hydrogen
e- Force p Planetary Model Since electron orbits the proton, a force exists.
e- Acceleration p Planetary Model • Force implies acceleration • Accelerating charges emit light • Light carries energy (E = hf)
e- p Planetary Model Electron moves closer to the nucleus since it requires less energy to be there.
Planetary Model • But the electron is still accelerating • Must still be radiating energy (light) • Must move still closer to the nucleus • Electron will spiral into and collide with the nucleus (in about 10-8 seconds) Atoms do not exist!!
Bohr’s Hypotheses • Stable electron orbits exist where the electron does not lose energy.
Electrons can be here or here but not here p
Bohr’s Hypotheses • Transitions can occur between orbits so long as the electron ends up with the energy of the new level.
5 4 3 Energy 6563 Å photon 2 Hydrogen Absorption
5 4 Energy 3 6563 Å photon 2 Hydrogen Emission
Hydrogen Atom 5 4 -e 434 nm 3 2 656 nm -e 1 -e +P 486 nm 410 nm -e -e 400 nm 700 nm
Emission andAbsorption Lines • Lines come from electron transitions • Energy change either comes from (absorption) or is given to (emission) photon. E • Photon energy Frequency • E = hf • Frequency 1/(Wavelength) • f = c/l • Wavelength means COLOR
Brackett (Far IR) Paschen (IR) 4 3 Balmer (VIS) 2 1 Lyman (UV) Hydrogen Spectrum Energy
Aluminum Argon Calcium Carbon Helium Hydrogen Iron Krypton Magnesium Neon Nitrogen Oxygen Sodium Sulfur Xenon
Emission & Absorption Spectra for any Element • http://jersey.uoregon.edu/vlab/elements/Elements.html