Blackbody Radiation
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Transcript of Blackbody Radiation
Blackbody Radiation
Max Planck, Planck’s constant
Max Karl Ernst Ludwig Planck
Found an empirical formula which fit the measured blackbody curve
Looked for way to derive this empirical formula
Photo from http://www-groups.dcs.st-and.ac.uk/~history/PictDisplay/Planck.html
Max Planck, Planck’s constant
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Max Karl Ernst Ludwig Planck
Photo from http://www-groups.dcs.st-and.ac.uk/~history/PictDisplay/Planck.html
Disclaimer . . .
What did Einstein Win his Nobel Prize for?
photo from http://www.th.physik.uni-frankfurt.de/~jr/gif/phys/einst_7.jpg
The Photoelectric Effect
Photoelectric Effect Intuition What would a plot of current vs. light
intensity look like?
What would a plot of current vs. voltage look like?
What would a plot of threshold voltage vs. light frequency look like?
WHAT BROUGHT DOWN THE NEPHITES
200 years of peace after Christ's visit. Began to be Lamanites Costly Apparel Churches built to get gain Persecuted prophets who were doing
miracles Willful rejection of good
The Photoelectric Effect
The Photoelectric Effect
Wave Theory of Light and the Photoelectric Effect
Existence of a threshold voltageCurrent increases with intensity Threshold is a function of light
frequencyNo intensity thresholdNo time delayFairly monochromatic electron
energies
Einstein’s Explanation...
Plank was right!
photo from http://www.th.physik.uni-frankfurt.de/~jr/gif/phys/einst_7.jpg
Photons and Work Functions
Light is incident on a Zinc plate (Φ=4.31 eV). Only one of the following lights will cause the electrons to be emitted from the surface, which one is it. A. Infra-red
B. VisibleC. Ultra-violet
What is the velocity of the electrons coming off the
metal?
221 mv hf
A beam of ultra violet light is incident on the metal ball of an electroscope (hf > Φ) that is initially negatively charged. The electroscope . . .
Losses its negative charge.
A beam of visible light is incident on the metal ball of an electroscope (hf < Φ) that is initially negatively charged. The electroscope . . Nothing happens
—even after a long time.
Why does UV light give you a sunburn?
Discussion question: 400-nm wavelength light strikes a metal surface, a stream of electrons emerges from the metal. If the intensity of the light striking the surface is doubled, A. More electrons are emitted in a given
time interval.B. The electrons that are emitted are
more energetic.C. Both of the aboveD. Neither of the above
Discussion question: When 400-nm wavelength light strikes a metal surface, a stream of electrons emerges from the metal. If the 400-nm light is replaced with 300 nm and the lamp is adjusted so that the intensity of the light striking the surface is the same as it was for the 400-nm light. With the 300-nm light,A. More electrons are emitted in a given
time interval.B. The electrons that are emitted are
more energetic.C. Both of the aboveD. Neither of the above
Discussion question: A beam of ultra-violet light is incident on the metal ball of an electroscope that is initially uncharged. Does the electroscope acquire a charge?A. Yes, it acquires a positive charge.B. Yes, it acquires a negative charge.C. No, it does not acquire a charge.
Double Slit Interference
Single Photon Interference
X-Ray Tube
-+CathodeAnode
-FilamentTungsten
Target
)cos1( cmh
eif
In the Compton experiment, the wavelength of the scattered light is ______________ the wavelength of the incident light.A. Longer thanB. The same asC. Shorter than
Compton Scattering of a “Photon”
e-
Before
e-
After
Are you pondering whatI’m pondering?
Yes, but how will we ever get that many rubber bands?
No you buffoon! Why do youneed x-rays to see this?