Lesson 5: Photons
Overview:
Although classical physics says that light behaves as a wave, the discovery that light also has particle properties led to development of the laser and other breakthroughs in light technology. In this section, you will read about photons and the nature of light.
Curriculum Expectations:
Overall Expectations:
F1. Analyze, with reference to quantum mechanics and relativity, how the introduction of new conceptual models and theories can influence and/or change scientific thought and lead to the development of new technologies.
F2. Investigate special relativity and quantum mechanics, and solve related problems.
F3. Demonstrate an understanding of the evidence that supports the basic concepts of quantum mechanics and Einstein’s theory of special relativity.
Specific Expectations:
F1.1 Analyze the development of the two major revolutions in modern physics (e.g., the impact of the discovery of the photoelectric effect on the development of quantum mechanics; the impact of thought experiments on the development of the theory of relativity), and assess how they changed scientific thought.
F2.1 Use appropriate terminology related to quantum mechanics and special relativity, including, but not limited to: quantum theory, photoelectric effect, matter waves, time dilation, and mass–energy transformation.
F2.2 Solve problems related to the photoelectric effect, the Compton effect, and de Broglie’s matter waves.
F2.4 Conduct a laboratory inquiry or computer simulation to analyse data (e.g., on emission spectra, the photoelectric effect, relativistic momentum in accelerators) that support a scientific theory related to relativity or quantum mechanics.
F3.1 Describe the experimental evidence that supports a particle model of light (e.g., the photoelectric effect, the Compton effect, pair creation, de Broglie’s matter waves).
F1. Analyze, with reference to quantum mechanics and relativity, how the introduction of new conceptual models and theories can influence and/or change scientific thought and lead to the development of new technologies.
F2. Investigate special relativity and quantum mechanics, and solve related problems.
F3. Demonstrate an understanding of the evidence that supports the basic concepts of quantum mechanics and Einstein’s theory of special relativity.
Specific Expectations:
F1.1 Analyze the development of the two major revolutions in modern physics (e.g., the impact of the discovery of the photoelectric effect on the development of quantum mechanics; the impact of thought experiments on the development of the theory of relativity), and assess how they changed scientific thought.
F2.1 Use appropriate terminology related to quantum mechanics and special relativity, including, but not limited to: quantum theory, photoelectric effect, matter waves, time dilation, and mass–energy transformation.
F2.2 Solve problems related to the photoelectric effect, the Compton effect, and de Broglie’s matter waves.
F2.4 Conduct a laboratory inquiry or computer simulation to analyse data (e.g., on emission spectra, the photoelectric effect, relativistic momentum in accelerators) that support a scientific theory related to relativity or quantum mechanics.
F3.1 Describe the experimental evidence that supports a particle model of light (e.g., the photoelectric effect, the Compton effect, pair creation, de Broglie’s matter waves).
Success Criteria:
- Why is energy required to remove electrons from the atoms?
- What is the name of the minimum energy required to remove a single electron from a piece of metal?
- How do you convert electron volts, eV, into Joules?
- How do you calculate the work function, W, in terms of the electric potential difference that is able to eject electrons?
- Describe the photoelectric effect and what it means to have a threshold frequency.
- What two difficulties did physicists have when they tried to explain the results of photoelectric experiment using the classical wave theory of light?
- What are two important properties of photons?
- What is Planck's constant?
- If a photon has a higher frequency and thus a greater, the extra energy above the work function goes into kinetic energy of the electron. Write the linear expression to represent this relationship.
- How do you calculate the momentum and energy of a photon?
Time Allocation: 4 hours
Learning Activities:
Read pages 620 - 630 from Nelson 12.2
In the playlist below, video:
- Will show you how to find the kinetic energy of a photon required to set an electron from sodium free.
- Will show you how to find wavelength of a photon required to set an electron from nickle free.
- Will show you how to find the eventual velocity of the electron from silicon set free by a photon.
- Will show you how to find the momentum of a photon. And find out how can a mass-less photon have momentum?
- Albert Einstein: Why Light is Quantum
Practice questions 1 and 2 on page 624.
Practice questions 1, 2, and 3 on page 626.
Practice questions 1, 2, and 3 on page 626.
Task:
Solve questions 1 and 3 from Nelson 12.2 Review on page 631.
Optional Extension:
Optional Extension:
- Solve question 6 on page 631.
Reflect:
Describe the experimental evidence that supports a particle model of light (e.g., the photoelectric effect, the Compton effect, pair creation, de Broglie’s matter waves).
