Final answer:
The photoelectric effect and thermionic emission are different processes; the former relies on photon energy and the latter on thermal energy. Both assertions about the independence of photoelectric effect from temperature and the temperature-dependence of thermionic emission are correct, confirming option 'a' as true.
Step-by-step explanation:
The assertion and the reason provided in the student's question address two different phenomena responsible for the emission of electrons from a material. The assertion states that photoelectric emission is different from thermionic emission, which is true. Photoelectric emission occurs when electrons are ejected from a material due to the absorption of energy from photons, which is dependent on the frequency but not the intensity of the incoming light. On the other hand, thermionic emission is the release of electrons due to the thermal energy of the material, which requires a high temperature to overcome the work function of the electrons.
The reason given is that thermionic emission is temperature-dependent, while photoelectric emission is temperature-independent. The photoelectric effect does not rely on the temperature of the material, but rather on the energy of the photons. Therefore, the reason is indeed true and helps to differentiate the two processes.
In conclusion, the assertion (a) and the reason are both true, and the reason is the correct explanation of the assertion, making option 'a' the correct answer to the initial question.