Final answer:
In summary, the true statement is that increasing the light intensity on a piece of metal will increase the number of electrons ejected assuming the frequency is above the threshold, and when an electron drops to the ground state, a photon is emitted. However, hotter objects actually have a higher peak frequency, and decreasing a photon's frequency decreases its momentum. Answer number b and d is correct.
Step-by-step explanation:
The student's question pertains to the photoelectric effect and the behavior of photons and electrons in different circumstances. Here's a breakdown of the true statements:
- Hotter objects have a smaller peak frequency: False. Hotter objects emit radiation with a higher peak frequency, not smaller, according to Planck's law.
- Increasing the light intensity on a piece of metal will increase the number of electrons ejected (assuming f>fo): True. As the intensity of light increases, more photons hit the metal surface, thus more electrons can be ejected provided the frequency of the light is above the threshold frequency.
- Decreasing a photon's frequency increases its momentum: False. The momentum of a photon is directly proportional to its frequency, so decreasing the frequency actually decreases its momentum.
- If an electron drops down to the ground state, a photon will be emitted: True. This emission occurs as the electron releases energy equal to the difference between the higher energy level and the ground state.