Final answer:
To generate a current in a photoelectric cell, photons must eject electrons from the metal with sufficient energy, determined by the photon's frequency rather than intensity. The photoelectric effect occurs instantly if the photon frequency is above a threshold, while no electrons are emitted below this frequency.
Step-by-step explanation:
In order for a current to flow in a photoelectric cell, a photon of light must eject an electron in the metal. For this to occur, the energy of the photon must be equal to or greater than the energy needed to remove the electron from its energy state. It is the frequency of the incident light that is important, not its intensity.
When light strikes the metal cathode, if the energy of the photons is sufficient, electrons are emitted and attracted to the anode, which results in a flow of electrical current. The photoelectric effect occurs instantly when the light has a frequency above a certain threshold that provides enough energy for electrons to be ejected; the intensity of the light determines how many electrons are ejected but not their kinetic energy.
The phenomenon can be observed by irradiating a metal surface with photons. If the frequency of the photons matches or exceeds the threshold frequency, the electrons are ejected, and if this frequency is below the threshold, no electrons are emitted. Albert Einstein proposed that the energy of a photon, given by the equation E = hv, where E is the energy, h is Planck's constant, and v is the frequency, must be high enough to overcome the metallic bond holding the electron, leading to the emission of the electron.