origin of quantum theory black body radiation photoelectric effect compton scattering
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Origin of Quantum Theory
Black Body Radiation
Photoelectric Effect
Compton Scattering
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Origins of Quantum TheoryWho first postulated the idea of light quanta?
1. Planck2. Bohr3. De Broglie4. Einstein5. Heisenberg
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Origins of Quantum TheoryWho first postulated the idea of light quanta?
1. Planck2. Bohr3. De Broglie4. Einstein5. Heisenberg
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Origins of Quantum TheoryIn the photoelectric effect experiment, current flows when the light frequency is
1. less then the threshold frequency.2. equal to the threshold frequency.3. greater then the threshold frequency.4. less than the cathode’s work function.5. equal to the cathode’s work function.
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Origins of Quantum TheoryIn the photoelectric effect experiment, current flows when the light frequency is
1. less then the threshold frequency.2. equal to the threshold frequency.3. greater then the threshold frequency.4. less than the cathode’s work function.5. equal to the cathode’s work function.
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Origins of Quantum TheoryThe minimum amount of energy needed to free an electron from a piece of metal is called the
1. Gibb’s free energy.2. quantum energy.3. liberation potential.4. threshold energy.5. work function.
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Origins of Quantum TheoryThe minimum amount of energy needed to free an electron from a piece of metal is called the
1. Gibb’s free energy.2. quantum energy.3. liberation potential.4. threshold energy.5. work function.
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Origins of Quantum Theory
Blackbody RadiationPlanck(1900)
En = nhf
Photoelectric EffectA. Einstein
(1905)Bohr Atom
N. Bohr(1911)
Compton scatteringCompton(1923)
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Origins of Quantum Theory Introduction to Radiation
Hot Solid
Hot Gas
Cold Gas
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Origins of Quantum Theory Spectra
Emission or Line spectra
Absorption spectra
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Origins of Quantum Theory This is one way we identify interstellar elements.
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Origins of Quantum Theory
What happens when you turn on the electric bunner on a stove?
Blackbody Radiation
Demonstration - light bulb filament Demonstration - idea blackbody
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Origins of Quantum Theory How was the spectra measured?
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Origins of Quantum Theory Here is what they knew at the turn of the century.
The total power radiated is
The wavelength for maximum radiation is inversely proportional to the temperature
The distribution of wavelengths depends
on the temperature only, not the material.
maxT 2.898X10 3 mK
R ,T
AP
I power
area
Pblackbody AT 4
5.67X10 8 W m2K 4
area under curve
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Origins of Quantum TheoryT = ________ max = ________
max T = ________
T = ________ max = ________
max T = ________
T = ________ max = ________
max T = ________
What do you notice about these values?
6,000 K
5,000 K
7,000 K 425 nm
485 nm
3.0X10-3 mK
3.0X10-3 mK
3.0X10-3 mK
600 nm
They all have the same value.
maxT 2.898X10 3 mK
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Origins of Quantum Theory
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Origins of Quantum Theory Classical Theory (Maxwell’s Electromagnetic Theory)
Planck’s Theory (Quanta)
E nhf
ultraviolet catastrophe
12
),(5
2
kThcehc
TR
R(,T) 2ckT
4
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Origins of Quantum Theory Photoelectric Effect
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Origins of Quantum Theory
Ebefore Eafter
eKEEhf 0
stoppinge eVKE
fe
h
e
EVstopping 0
E0 is the work function or binding energy
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Origins of Quantum Theory
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Origins of Quantum Theory
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Origins of Quantum Theory
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Origins of Quantum Theory
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Origins of Quantum Theory
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Origins of Quantum Theory
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Origins of Quantum Theory
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Origins of Quantum Theory
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Origins of Quantum Theory
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Origins of Quantum Theory
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Origins of Quantum Theory
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Origins of Quantum Theory
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Origins of Quantum TheoryThe work function of metal A is 3.0 eV. Metals B and C have work functions of 4.0 eV and 5.0 eV, respectively. Ultraviolet light shines on all three metals, creating photoelectrons. Rank in order, from largest to smallest, the stopping voltages for A, B, and C.
1. VA > VB > VC 2. VC > VB > VA 3. VA = VB = VC
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Origins of Quantum TheoryThe work function of metal A is 3.0 eV. Metals B and C have work functions of 4.0 eV and 5.0 eV, respectively. Ultraviolet light shines on all three metals, creating photoelectrons. Rank in order, from largest to smallest, the stopping voltages for A, B, and C.
1. VA > VB > VC 2. VC > VB > VA 3. VA = VB = VC
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Origins of Quantum TheoryThe intensity of a beam of light is increased but the light’s frequency is unchanged. Which of the following is true?
1. The photons travel faster.2. Each photon has more energy.3. There are more photons per second. 4. The photons are larger.
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Origins of Quantum TheoryThe intensity of a beam of light is increased but the light’s frequency is unchanged. Which of the following is true?
1. The photons travel faster.2. Each photon has more energy.3. There are more photons per second. 4. The photons are larger.
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Origins of Quantum Theory Compton Scattering
scattered incident h
mc1 cos
scattered
incident
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Origins of Quantum Theory Compton Scattering
scattered incident h
mc1 cos
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Origins of Quantum Theory Classical Scattering of Electromagnetic Wave
So the radiation wavelength is the same as the incident wavelength.
We do not have to consider the magnetic field since it is so small compared to the electric field
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Origins of Quantum Theory Compton Scattering
Answer the first three questions in the tutorial and draw the diagram for the scattering experiment.
Discuss the Compton experiment in your group. What are the two physical quantities in the collision?
What is the assumption for light that Compton used?
That light behaved like a particle with energy
And momentum
E hf
p E
c
hf
c
E2 pc 2 mc
2 2 m 0
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Origins of Quantum Theory Compton Scattering What two equations (conservation law) did Compton use to
find the change in wavelength?
Draw the collision between the electron and the photon. Label the angles and .
Conservation of energyConservation of momentum
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Origins of Quantum TheoryWrite the energy and momentum for each before and after
the collision
Conservation of Energy
Conservation of Momentum
fefpieip EEEE ,,,,
cos2 ,,
2
,
2
,
2
fpipfpipe ppppp efpip ppp
,,
2222 mccphfcmhf efei
ipp ,
fpp ,
ep
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Origins of Quantum TheoryWrite the energy and momentum for each before and after
the collision
before after
electron
photon
E e,i
Ee, f
pe,i
pe, f
E p,i
pp,i
E p, f
pp, f
2cme
222 cmE ee
i
iip hc
hfc
E
,
ihffhf
f
ffp hc
hf
c
E
,
0
?
scattered incident h
mc1 cos
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Origins of Quantum Theory
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Origins of Quantum Theory Introduction to Radiation
Solid
Hot Gas
Cold Gas
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Origins of Quantum Theory Planck’s Theory (Quanta)
R(,T) 2hc 2
5 ehc kT 1
kTc
hckThc
kThc
hc
ehc
TRkThc
45
2
5
2
5
2
22
11
2
12
),(
Classical expression
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Origins of Quantum Theory Planck’s Theory (Quanta)
R(,T) 2hc 2
5 ehc kT 1
kThc
kThc
kThc
ehc
ehc
ehc
TR
5
2
5
2
5
2
22
12
),(
0
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Origins of Quantum Theory Optical Pyrometer
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Origins of Quantum Theory Microwave Cosmic Background
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Origins of Quantum Theory
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Origins of Quantum Theory Use the results above and substitute into the conservation
equation.
Do the same for conservation of momentum in the x direction.
Now for momentum in the y direction.
Compton solved these three equations to find = - . Where is the initial wavelength for the photon and is the final wavelength for the photon.
What is the final results (Compton’s equation) that Compton found?
scattered incident h
mc1 cos