(UEMG 2019) - Question Medium of Physics

Read the following excerpt: The photoelectric effect was discovered in 1886 by the German physicist Heinrich Hertz (1857-1894). At the time, Hertz noticed that the incidence of ultraviolet light on metal plates assisted in the production of sparks. The theoretical explanation for the photoelectric effect, however, was only presented by the German physicist Albert Einstein in 1905. The doubt that existed at the time was related to the kinetic energy of the electrons that were ejected from the metal: this magnitude did not depend on the ... of the incident light. Einstein realized that the agent responsible for ejecting each electron was a single photon, a particle of light that transferred to the electrons a part of its energy, ejecting it from the material, provided that its ... was large enough for such.