Planck’s hypothesis, and Einstein’s photon theory. Contents: Hubris at the turn of the century...
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Planck’s hypothesis, and Einstein’s photon theory. Contents: •Hubris at the turn of the century •Black Body radiation •The problem with black body radiation •Planck’s hypothesis •Einstein’s corpuscular light theory
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Transcript of Planck’s hypothesis, and Einstein’s photon theory. Contents: Hubris at the turn of the century...
Planck’s hypothesis, and Einstein’s photon theory.
Contents:•Hubris at the turn of the century•Black Body radiation•The problem with black body radiation•Planck’s hypothesis•Einstein’s corpuscular light theory•Photons : Example 1 | Example 2
•Whiteboards
Hubris
TOC
•1900 +/- 10.•The end of physics•Tricky bits
•Motion of the earth with respect to “ether”•(Einsteinian relativity)
•Black body radiation•(Quantum mechanics)
Black Body radiation
TOC
Radiation given off by hot stuff
Black Body radiation
TOC
The problem
fig 27-5
Black Body radiation
TOC
Planck’s solution
Planck proposes a quantum hypothesisEmin = hf
h = Planck’s constant = 6.626 x 10-34 Jsf = frequency of oscillations (Hz, s-1)
E = nhf, n = 1,2,3,...Hypothesis fits data exactly.Planck thinks it’s just math, not reality
Einstein’s photon theory
TOC
Einstein:Reality is quantumRadiation is also quantizedPhotons = corpuscular theory
E = hf v = fE = Photon energy (Joules)v = c = speed of light = 3.00 x 108 m/sf = frequency (Hz) = wavelength (m)
TOC
E = hf v = fE = Photon energy (Joules)v = c = speed of light = 3.00 x 108 m/sf = frequency (Hz) = wavelength (m)
Example 1: What is the energy of a 460 nm photon?v = f, c = f, f = c/E = hf = hc/
TOC
E = hf v = fE = Photon energy (Joules)v = c = speed of light = 3.00 x 108 m/sf = frequency (Hz) = wavelength (m)Example 2: A photon has an energy of 13 eV. What is its wavelength? (Remember V = W/q, and 1 eV is one electron moved through 1 volt)E (in Joules) = (13 eV)(1.602 x 10-19 J/eV)c = f, = c/fE = hf, f = E/h = c/f = hc/E
Whiteboards: Photons
1 | 2 | 3 | 4
TOC
4.36 x 10-19 J W
E = hf = (6.626 x 10-34 Js)(6.58 x 1014 s-1) = 4.36 x 10-19 J
What is the energy of a photon with a frequency of 6.58 x 1014 Hz?
8.23 x 1015 Hz, 36.5 nm W
E = hf f = E/h = (5.45 x 10-18 J)/(6.626 x 10-34 Js) = 8.23 x 1015 Hzv = f, = v/f = (3.00 x 108 m/s)/(8.23 x 1015 Hz) = 36.5 nm
What is the frequency of a photon with an energy of 5.45 x 10-18 J?What is its wavelength?
6.33 x 10-19 J, 3.95 eV W
E = hf = hc/1eV = 1.602 x 10-19 JE = hc/= (6.626 x 10-34 Js)(3.00 x 108 m/s)/(3.14 x 10-9 m) = 6.33 x 10-19 J
E = (6.33 x 10-19 J)/(1.602 x 10-19 J/eV) = 3.95 eV
What is the energy in Joules of a 314 nm photon? What is that energy in eV? (2)
206 nm W
E = hf = hc/1eV = 1.602 x 10-19 JE = (6.02 eV)(1.602 x 10-19 J/eV) = 9.64 x 10-19 JE = hc/, = hc/E= (6.626 x 10-34 Js)(3.00 x 108 m/s)/(9.64 x 10-19 J) = 2.06 x 10-7 m = 206 nm (nm = 1 x 10-9 m)
A photon has an energy of 6.02 eV. What is its wavelength?(answer in nm) (2)
9.36 x 1017 photons/sec W
E = hf = hc/In one second, a 300 mW laser emits photons with a total energy of .300 JE = hc/,= (6.626 x 10-34 Js)(3.00 x 108 m/s)/(620. x 10-9 m) = 3.20613 x 10-19 J (per photon) # photons = (.300 J/s)/(3.20613 x 10-19 J/photon) = 9.36 x 1017 photons/secHey, that’s a lot!
How many photons per second stream from a 620. nm, 300. mW laser? (2)
Waves Photons
Color
Brightness
Energy per photon changesE = hfX-Rays, UV, Gamma
Wavelength Changes
Amplitude Changes # of photons changesmany = brightfew = dimCCD Devices, High speed film
big = red
small = blue
small = dim
big = bright
Light
