Warm Up: n/a
Learning Goals:
As you work through this unit, you should be able to understand and demonstrate these Big Ideas:
Today:
Photoelectric Effect - Answer to the riddle caused by the sim:
Assignment:
Learning Goals:
As you work through this unit, you should be able to understand and demonstrate these Big Ideas:
- How do emission and absorption spectra occur?
- How does the photoelectric effect exemplify the particle nature of light, and how does the de Broglie hypothesis suggest the wavelike nature of particles
- How are the concepts of momentum and energy in collisions applied to the scattering of photons by electrons?
- How are mass–energy equivalence and charge and nucleon conservation laws applied to nuclear reactions?
Today:
Photoelectric Effect - Answer to the riddle caused by the sim:
- Not every photon emits an electron, even if the photons have enough energy to emit electrons. If a photon is absorbed by an electron with binding energy greater than the photon energy, the electron will not be released. Photons with higher energies are more likely to release electrons because a greater proportion of the electrons in the metal have binding energy less than the photon energy. Therefore, as you increase the frequency, the number of emitted electrons (and therefore the current) will increase until all photons are emitting electrons. Note that this behavior is different from the simplified model used by many textbooks, in which every photon with frequency greater than the threshold frequency releases an electron, so the current is constant above the threshold frequency.
- In the default setting, since the intensity of light is proportional to the number of photons times the frequency, if you increase the frequency while holding the intensity constant, the number of photons will decrease. Therefore, if you increase the frequency past the point where all photons are emitting electrons (see previous bullet), the number of emitted electrons (and therefore the current) will start to decrease. Note that this is different from the simplified model used by many textbooks, in which current is constant above the threshold frequency. If you want to be able to change the frequency without changing the number of photons, select “Control photon number instead of intensity” in the Options menu.
- ConcepTest Questions
Assignment:
- Practice 27.3: READ FOR UNDERSTANDING 27.1-27.4. Complete the MasteringPhysics assignment.
- Practice 27.4, due Friday 4/8: READ FOR UNDERSTANDING 27.5-27.6
- Practice 27.5, due Monday 4/11: READ FOR UNDERSTANDING 27.7-27.8