When light shines on a metal, electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect. This process is also often referred to as photoemission, and the electrons that are ejected from the metal are called photoelectrons.
Few common terms
Photoelectron : The electron emitted in photoelectric effect is called photoelectron.
Photoelectric current : If current passes through the circuit in photoelectric effect then the current is called photoelectric current.
Work function : The minimum energy required to make an electron free from the metal is called work function. It is constant for a metal and denoted by φ or W. It is the minimum for Cesium. It is relatively less for alkali metals.
Saturation current: When all the photo electrons emitted by cathode reach the anode then current flowing in the circuit at that instant is known as saturated current, this is the maximum value of photoelectric current.
Stopping potential : Minimum magnitude of negative potential of anode with respect to cathode for which current is zero is called stopping potential. This is also known as cutoff voltage.
Laws of Photoelectric emission
For a light of any given frequency, photoelectric current is directly proportional to the intensity of light, provided the frequency is above the threshold frequency.
For a given material, there is a certain minimum (energy) frequency, called threshold frequency, below which the emission of photoelectrons stops completely, no matter how high the intensity of incident light.
The maximum kinetic energy of the photoelectrons is found to increase with increase in the frequency of incident light, provided the frequency exceeds the threshold limit. The maximum kinetic energy is independent of the intensity of light.
The photo-emission is an instantaneous process. After the radiation strikes the metal surface, it just takes 10to power –9 s for the ejection of photoelectrons.
Below is the simulation of photoelectric effect. Play with by moving the sliders and try answer the questions asked below to check your grasp in the topic.