A Level Physics Practice Exam

Why do electrons not get emitted if the frequency of radiation is below a certain value?

1. Because the radiation does not have enough intensity

2. Because the energy of the photon is less than the work function

3. Because electrons are bound too tightly to be emitted

4. Because the radiation is absorbed rather than emitted

The correct answer is: Because the energy of the photon is less than the work function

The emission of electrons from a material, commonly referred to as the photoelectric effect, is contingent upon the energy of the incoming photons. Each photon carries energy directly proportional to its frequency, given by the equation E = h*f, where E is the energy of the photon, h is Planck's constant, and f is the frequency. For an electron to be emitted from a surface, the energy of the incoming photon must meet or exceed a specific threshold known as the work function of the material. The work function is the minimum energy required to remove an electron from the surface of a material. When the frequency of the radiation is below a certain threshold, the energy of the photons is too low to overcome the work function, which means that no electrons will be emitted. This fundamental relationship highlights that it is not merely the intensity of the radiation that matters, but rather the energy associated with the frequency. In this context, the other choices suggest alternative reasons for the absence of electron emission, but they do not correctly address the underlying principle of photon energy relative to the work function. Therefore, the key concept to understand here is that the frequency of the radiation must be sufficiently high to provide the photons with adequate energy to release electrons from the material.