Final answer:
The photoelectric effect is not limited to visible light; it can be caused by any high frequency EM radiation with sufficient photon energy, highlighting the particle nature of EM radiation.
Step-by-step explanation:
The photoelectric effect can be caused by various types of electromagnetic (EM) radiation, not just visible light. The key factor that determines whether EM radiation can cause the photoelectric effect is the energy of the photons, which is related to their frequency.
High frequency EM radiation photons, such as ultraviolet light and X-rays, have more energy and can cause the photoelectric effect. In contrast, low frequency EM radiation photons, like radio waves, generally do not have enough energy to eject electrons from materials.
As for the nature of the photoelectric effect, it is a direct consequence of the particle character of EM radiation. This was one of the key observations that led to the development of quantum mechanics. It is described by the emission of electrons from a material when it is exposed to EM radiation of sufficient energy (above a certain threshold frequency) and contradicts the classical wave theory of light.