example of black body spectra for different temperatures
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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
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
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
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=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)
Configuration Prediction (Classical)
Observation
Brighter Light
Very Bright Red Light
Change Color
Time until emission of electricity
Metal
Configuration Prediction (Classical)
Observation
Brighter Light More Electricity Faster electrons
Very Bright Red Light
More Electricity
Change Color No Effect
Time until emission of electricity
Few Seconds Metal
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 of electricity
Few Seconds
Instantaneous (~10-9 s) Metal
Robert Millikan 1868-1953 Nobel Prize in Physics 1923
"for his services to Theoretical Physics, and especially for his discovery of 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 of energy quanta".
Diagram of Millikan’s Device For measuring photoelectric effect
Data from Millikan’s 1916 Article
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
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
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
