Download - Properties of Light The Speed of Light Galileo’s Experiment A B c = Round Trip Distance/Total Time
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Properties of LightProperties of Light
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The Speed of LightThe Speed of Light
Galileo’s Experiment
AB
c = Round Trip Distance/Total Time
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Ole Roemer (1675)Ole Roemer (1675)
Earth
Jupiter
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Speed of LightSpeed of Light
From Roemer’s Experimentc = Diameter of Orbit/Time Delay
Modern Valuec = 299,792.458 km/sec
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Speed of LightSpeed of Light
Absolute constant
Nothing travels faster
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Relative VelocitiesRelative VelocitiesOur 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 = 0v
v
v v Vrel = 2v
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Try it with LightTry it with Light
Sun
½ c
c
Intuition says you get ½ cEinstein says c
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Try it with Light
Sun½ c
c
Intuition says you get 1½ cEinstein says c
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Nature of LightNature of Light
Particle?Newton
Wave?Christian Huygens in Newton’s dayThomas Young (1801)
Light can diffract - must be a waveTransverse wave
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Types of WavesTypes of Waves
Transverse and Longitudinal
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WavelengthWavelength
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Electromagnetic Electromagnetic SpectrumSpectrum
Increasing Wavelength
Visible Light
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The Visible SpectrumThe Visible Spectrum
400nm 500nm 600nm 700nm
Wavelength means
COLOR
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FrequencyFrequency
Number of complete events occurring in a period of timeWaves/second
ExamplesSecond hand on a clock?
1 cycle/minute = 1/60 cycle/secUS Presidential Electons
1 election/4 years = 1/4 election/year
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Frequency and PeriodFrequency and Period
Period =
1
Frequency
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Speed, Wavelength, Speed, Wavelength, FrequencyFrequency
c = f
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Photon EnergyPhoton Energy
E f
E = hf
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Properties of LightProperties of LightSpeed (c)
Nothing travels faster
Absolute constantWavelength ()
Gamma rays, X-rays, UV, Visible, IR, Radio
In visible wavelength means colorFrequency (f)
Number of complete waves per secondEnergy of a Photon (E)
E = hf
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Dispersive Element
Basic SpectrographBasic Spectrograph
Collimating Lens
Recording Device
Slit
Imaging Lens
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Mercury near HorizonMercury near Horizon
The atmosphere can act like a prism
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Continuous SpectrumContinuous Spectrum
Source must be HOT and DENSE
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Emisson (Bright Line) Emisson (Bright Line) SpectrumSpectrum
Source must be HOT and TENUOUS
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Absorption SpectrumAbsorption Spectrum
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Types of SpectraTypes of Spectra
Continuous
Emission
Absorption
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Rutherford Scattering Rutherford Scattering ExperimentsExperiments
Atom
He “bullet”
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Hydrogen AtomsHydrogen Atoms
Simplest atomOne proton, one electron
Most abundant atom90% of universe is hydrogen
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Planetary ModelPlanetary Model
Force
p
e-
Since electron orbits the proton, a force exists.
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Planetary ModelPlanetary Model
p
e-
Acceleration
•Force implies acceleration
•Accelerating charges emit light
•Light carries energy (E = hf)
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Planetary ModelPlanetary Model
p
e-
Electron moves closer to the nucleus since it requires less energy to be there.
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Planetary ModelPlanetary Model
But the electron is still acceleratingMust still be radiating energy (light)Must move still closer to the nucleusElectron will spiral into and collide with
the nucleus (in about 10-8 seconds)
Atoms do not exist!!
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Bohr’s HypothesesBohr’s Hypotheses
Stable electron orbits exist where the electron does not lose energy.
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Electrons can be here or
here
but not here
p
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Bohr’s HypothesesBohr’s Hypotheses
Transitions can occur between orbits so long as the electron ends up with the energy of the new level.
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HydrogenHydrogen
Energy
2
345
6563 Å photon
Absorption
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HydrogenHydrogen
Energy
2
345
6563 Å photon
Emission
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+P+P
22
33
44
656 nm
700 nm700 nm400 nm400 nm
-e-e
Hydrogen Hydrogen AtomAtom
11
-e-e
-e-e
55
-e-e
486 nm
434 nm
-e-e410 nm
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Emission andEmission andAbsorption LinesAbsorption Lines
Lines come from electron transitionsEnergy change either comes from
(absorption) or is given to (emission) photon. E
Photon energy FrequencyE = hf
Frequency 1/(Wavelength)f = c/
Wavelength means COLOR
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Hydrogen SpectrumHydrogen Spectrum
Energy
1
2
34
Lyman (UV)
Balmer (VIS)
Paschen (IR)
Brackett (Far IR)
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Aluminum
Oxygen
Argon
Calcium
Carbon
Helium
Hydrogen
Iron
Krypton
Magnesium
Neon
Nitrogen
Sulfur
Sodium
Xenon
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Emission & Absorption Emission & Absorption Spectra for any ElementSpectra for any Element
http://jersey.uoregon.edu/vlab/elements/Elements.html
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Review
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End of LightEnd of Light