Josef Stefan (1835-1893) • Total energy radiated proportional to T4 Question: Suppose temperature raised from 300K (room temp) to 6000K (sun) By what factor does the energy radiated increase? A. B. C. D.
16 16,000 90,000 160,000
Josef Stefan (1835-1893) • Total energy radiated proportional to T4 Question: Suppose temperature raised from 300K (room temp) to 6000K (sun) By what factor does the energy radiated increase? A. B. C. D.
16 16,000 90,000 160,000 Answer: (6000/300)4 = 204=160,000
Question: Wavelength of emitted radiation (light) changes as objects get hotter. • 1. Hotter -> Longer Wavelength • 2. Hotter -> Shorter Wavelength
Question: Wavelength of emitted radiation (light) changes as objects get hotter. • 1. Hotter -> Longer Wavelength • 2. Hotter -> Shorter Wavelength
Steam Radiator 400K Very Hot Stove 900K Lava ~2000K Sun 6000K
IR Dull Red (transition to visable) Glowing (most radiation still in IR) Most radiation visable
Wilhelm Wien
Wilhelm Wien (18643-1928) Nobel Prize 1911
Example of Black Body Spectra for different temperatures
Below is a photo of three stars. The light emitted by these stars is thermal radiation. Which of these stars is the hottest? The coolest? A. Red, yellow B. Red, blue C. Yellow, blue D.Blue, red E. Blue, yellow © 2007 W.W. Norton & Company, Inc. Physics for Engineers and Scientists
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Below is a photo of three stars. The light emitted by these stars is thermal radiation. Which of these stars is the hottest? The coolest? A. Red, yellow B. Red, blue C. Yellow, blue D.Blue, red E. Blue, yellow © 2007 W.W. Norton & Company, Inc. Physics for Engineers and Scientists
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Spectrum of high energy particle radiation from space does not follow a black body spectrum Cosmic Ray Flux
Above 1020 eV Very low flux ~ 1 particle per km2/sr/century
GeV 109
TeV 1012
PeV 1015
EeV 1018
1 Joule
ZeV 1021
What is the best known example of a black body source?
What is the best known example of a black body source? Hint
Temperature = 2.7 K
Cosmic Microwave Background (Radiation from Big Bang! T=2.725K. The theoretical curve obscures the data points and the error bars.
Astrophysical Journal, 473, 576
Black Body Radiation and the experimental basis for Quantum Theory
What is the energy of a “quanta” of RED light? 660 nm wavelength in units of electron volts?
E=hν h=6.62x10-34 Js
What is the energy of a “quanta” of RED light? 660 nm wavelength in units of electron volts?
E=hν h=6.62x10-34 Js ν=c/λ=3x108m/s/660x10-9m =4.54x1014 s-1 E= 6.62x10-34Js x 4.54x1014 s-1 E= 3.01 x 10-19 J 1eV= 1.602 x10-19 J E=3.01x10-19J/1.602x10-19J/eV E=1.88 eV
What is the energy of a “quanta” of RED light? 660 nm wavelength in units of electron volts?
E=hν h=6.62x10-34 Js ν=c/λ=3x108m/s/660x10-9m =4.54x1014 s-1 E= 6.62x10-34Js x 4.54x1014 s-1 E= 3.01 x 10-19 J 1eV= 1.602 x10-19 J E=3.01x10-19J/1.602x10-19J/eV E=1.88 eV
What is the energy of a “quanta” of RED light? 660 nm wavelength in units of electron Volts
Easier Way to Solve this E=hc/λ hc=1240 eV nm (useful constant to remember) E=(1240/660)eV E= 1.88 eV
Question: What is the energy quantization of a grandfather clock? Hint:
Question: What is the energy quantization of a grandfather clock? Hint:
Question: What is the energy quantization of a grandfather clock? Hint:
E=nhν for n=1, ν=1Hz=1s-1 E= 6.6x10-34J
E=nhν for n=1, ν=1Hz=1s-1 E= 6.6x10-34J
How is the quantization realized?
E=nhν for n=1, ν=1Hz=1s-1 E= 6.6x10-34J
How does this quantization translate into quantization of the pendulum displacement (height)?
E=nhν for n=1, ν=1Hz=1s-1 E= 6.6x10-34J
How does this quantization translate into quantization of the pendulum displacement (height)? E=mgH=6.6x10-34J
H
H=6.6x10-34J/(1kg 10m/s2)=6.6x10-35m Too small to measure (size of an atom is about 10-8 m)