1. Origin of Quantum Theory
Black Body Radiation
Photoelectric Effect
Compton Scattering

2. Who first postulated the idea of light quanta?
1. Planck
2. Bohr
3. De Broglie
4. Einstein
5. Heisenberg

3. Who first postulated the idea of light quanta?
1. Planck
2. Bohr
3. De Broglie
4. Einstein
5. Heisenberg

4. In 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.

5. In 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.

6. The 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.

7. The 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.

8. En = nhf Blackbody Radiation Planck (1900) Compton scattering Compton
(1923)
En = nhf
Photoelectric Effect
A. Einstein
(1905)
Bohr Atom
N. Bohr
(1911)

9. Introduction to Radiation
Hot Solid
Hot Gas
Cold Gas

10. Spectra
Absorption spectra
Emission or Line spectra

11. This is one way we identify interstellar elements.

12. Blackbody Radiation
Demonstration - light bulb filament
Demonstration - idea blackbody
What happens when you turn on the electric bunner on a stove?

13. How was the spectra measured?

14. 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.
power
area
area under curve

15. T = ________ lmax = ________
lmax T = ________
6,000 K
5,000 K
7,000 K
425 nm
485 nm
3.0X10-3 mK
600 nm
What do you notice about these values?
They all have the same value.

17. Classical Theory (Maxwell’s Electromagnetic Theory)
Planck’s Theory (Quanta)
ultraviolet catastrophe

18. Photoelectric Effect

19. E0 is the work function or binding energy

32. The work function of metal A is 3. 0 eV
The 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

33. The work function of metal A is 3. 0 eV
The 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

34. The 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.

35. The 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.

36. Compton Scattering

37. Compton Scattering

38. Classical Scattering of Electromagnetic Wave
We do not have to consider the magnetic field since it is so small compared to the electric field
So the radiation wavelength is the same as the incident wavelength.

39. 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

40. 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 energy
Conservation of momentum

41. Write the energy and momentum for each before and after the collision
Conservation of Energy
Conservation of Momentum

42. Write the energy and momentum for each before and after the collision
before after
electron
photon ?

44. Introduction to Radiation
Solid
Hot Gas
Cold Gas

45. Planck’s Theory (Quanta)
Classical expression

46. Planck’s Theory (Quanta)

47. Optical Pyrometer

48. Microwave Cosmic Background

50. 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?