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Example of Black Body Spectra for different temperatures What is the - - PowerPoint PPT Presentation
Example of Black Body Spectra for different temperatures What is the - - PowerPoint PPT Presentation
Example of Black Body Spectra for different temperatures 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 Planck Radiation Law Cosmic Microwave
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What is the best known example of a black body source?
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What is the best known example of a black body source? Hint Temperature = 2.7 K
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Astrophysical Journal, 473, 576 Cosmic Microwave Background (Radiation from Big Bang! T=2.725K. The theoretical curve obscures the data points and the error bars. Planck Radiation Law
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Question: What is the energy quantization
- f a grandfather clock?
Hint:
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Question: What is the energy quantization
- f a grandfather clock?
Hint:
E=nhν for n=1, ν=1Hz=1s-1 E= 6.6x10-34J
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How is the quantization realized?
E=nhν for n=1, ν=1Hz=1s-1 E= 6.6x10-34J
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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
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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 E=mgH=6.6x10-34J H=6.6x10-34J/(1kg 10m/s2)=6.6x10-35m H
Too small to measure (size of an atom is about 10-8 m)
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Configuration Prediction (Classical) Observation Brighter Light Very Bright Red Light Change Color Time until emission
- f electricity
Metal
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Configuration Prediction (Classical) Observation Brighter Light More Electricity Faster electrons Very Bright Red Light More Electricity Change Color No Effect Time until emission
- f electricity
Few Seconds Metal
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Configuration Prediction (Classical) Observation Brighter Light More Electricity Faster electrons YES NO Very Bright Red Light More Electricity No electricity Change Color No Effect Big Effect Time until emission
- f electricity
Few Seconds Instantaneous (~10-9 s) Metal
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Robert Millikan 1868-1953 Nobel Prize in Physics 1923 "for his services to Theoretical Physics, and especially for his discovery
- f the law of the
photoelectric effect" "for his work on the elementary charge of electricity and on the photoelectric effect" Albert Einstein 1879-1955 Nobel Prize in Physics 1921 Max Planck 1858-1947 Nobel Prize in Physics 1918
Emission and Absorption of Light evidence for quantization
"in recognition of the services he rendered to the advancement of Physics by his discovery
- f energy quanta".
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Diagram of Millikan’s Device For measuring photoelectric effect
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Data from Millikan’s 1916 Article
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- Phys. Rev. 7, 355–388 (1916)
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Example Problem The work functions for K and Zn are 2.26 eV and 4.24 eV Which will emit photoelectrons when illuminated by Red, Blue and UV light? Wavelength K (2.26 eV) Zn (4.24 eV) Red (700 nm) Blue (400 nm) UV (280 nm)
E=hν-w=0 hc=1240eV nm
Energy of photon is hν or hc/λ or 1240 eV nm/ λ
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Example Problem The work functions for K and Zn are 2.26 eV and 4.24 eV Which will emit photoelectrons when illuminated by Red, Blue and UV light? Wavelength K (2.26 eV) Zn (4.24 eV) Red (700 nm) Blue (400 nm) UV (280 nm)
E=hν-w=0 hc=1240eV nm
Energy of photon is hν or hc/λ or 1240 eV nm/ λ ? Photon Photoelectron? E= hc/λ If (hc/λ− w) > 0
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Example Problem The work functions for K and Zn are 2.26 eV and 4.24 eV Which will emit photoelectrons when illuminated by Red, Blue and UV light?
E=hν-w=0 hc=1240eV nm
Energy of photon is hν or hc/λ or 1240 eV nm/ λ ? Photon Photoelectron? E= hc/λ If (hc/λ− w) > 0 Wavelength K (2.26 eV) Zn (4.24 eV) Red (700 nm) 1.77 eV NO NO Blue (400 nm) 3.10 eV YES NO UV (280 nm) 4.42 eV YES YES
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