The phenomenon of photoelectric effect was discovered by Heinrich Hertz in 1887 and then it was extensively studied by several scientists like Hallwachs, Lenard, Millikan by performing a series of experiments they found that:When suitable radiations (visible light, ultra violet radiation etc) fall on a metallic surface, the electrons are emitted from it. This phenomenon is called the photoelectric effect. That’s the emission of electrons from metallic surface by light energy is called the photoelectric effect. The process of emission of electrons from metal by electromagnetic radiation is called photoelectric emission and the electrons so emitted are called the photoelectrons. Necessary condition for Photoelectric Effect:The frequency of incident radiation must be greater than a certain minimum frequency, called threshold frequency. Threshold frequency is different for different metals. The same condition can be put as the wavelength of incident radiation has to be smaller than the threshold wavelength. It can also be put as the energy of the incident photon has to be greater than the minimum energy required to eject the photoelectron. This energy is called the work function of the metal. Experimental study of Photoelectric Effect:The phenomenon of photoelectric effect may be demonstrated by a simple experiment. For this a metallic plate, a light source and a gold-leaf electroscope are taken. Light is made incident on a metallic plate and the plate is connected with negatively charged gold-leaf electroscope, it’s observed that the divergence of leaves of electroscope decreases; however if the metallic plate is connected to positively charged electroscope, the divergence of leaves increases. This shows that the metallic plate becomes positively charged. From this it’s clear that the negatively charged electrons escape from the metal plate. This is photoelectric effect. Salient features of Photoelectric effect:o For a given photosensitive material there is a minimum frequency of incident radiation below which emission of photoelectrons isn’t possible, whatever be intensity and duration of incident radiation. This frequency is called threshold frequency o The rate of emission of photoelectrons is directly proportional to the intensity of incident radiation o The maximum kinetic energy of the emitted photoelectrons increases with the increase of frequency of the incident radiation, however it does not depend on its intensity o As soon as radiation of appropriate frequency is incident on a photosensitive surface, the photo electrons are emitted instantly i e , there is no time lag between incident of radiation and emission of electrons. . . . . . . . . . . . . Electrons are one of the building block of an atom. An atom consists of protons and neutrons in the nucleus and electrons revolving around the orbit. Electrons have negative charge. Protons have positive charge and neutrons are charge less. Since electrons and protons are equal and opposite, an atom become charge less. The peculiarity of electrons is that they’re the charge carriers in an atom. The free electrons moves from one end to the other, hence the conduction occurs. In simple definition, Photon is nothing however the energy packets. It indicates the wave nature of a particle. This photon has energy and momentum. Let us go through more about the particle and the particle duality in detail. . . . . . . . . . .