Editing Content :: Admin Scraper

Chapter

Content type

Position

Value

structure of atom 41 by making an assumption that absorption and emmission of radiation arises from Max Planck oscillator i.e., atoms in the wall of black (1858–1947) body. Their frequency of oscillation is Max Planck,aGermanphysicist, received his Ph.D in theoretical changed by interaction with oscilators of physics from the University of electromagnetic radiation. Planck assumed Munich in 1879. In 1888, he that radiation could be sub-divided into discrete chunks of energy. He suggested that was appointed Director of the atoms and molecules could emit or absorb Institute of Theoretical Physics at the University of Berlin. energy only in discrete quantities and not Planck was awarded the Nobel Prize in Physics in a continuous manner. He gave the name in 1918 for his quantum theory. Planck also made quantum to the smallest quantity of energy significant contributions in thermodynamics and that can be emitted or absorbed in the form other areas of physics. of electromagnetic radiation. The energy (E) of a quantum of radiation is proportional Photoelectric Effect to its frequency (ν) and is expressed by In 1887, H. Hertz performed a very interesting equation (2.6). experiment in which electrons (or electric E = hυ (2.6) current) were ejected when certain metals The proportionality constant, ‘h’ is known (for example potassium, rubidium, caesium etc.) were exposed to a beam of light as shown as Planck’–34onstant and has the value in Fig.  2.9. The phenomenon is called 6.626×10 J s. Withthistheory,Planckwasabletoexplain Photoelectric effect. The results observed in this experiment were: the distribution of intensity in the radiation (i) The electrons are ejected from the metal from black body as a function of frequency or wavelength at different temperatures. surface as soon as the beam of light strikes the surface, i.e., there is no time Quanti sation has been compared to lagbetweenthestrikingoflightbeamand standing on a staircase. A person can stand the ejection of electrons from the metal on any step of a staircase, but it is not possible for him/her to stand in between the two steps. surface. The energy can take any one of the values (ii) The number of electrons ejected is proportionaltotheintensityorbrightness from the following set, but cannot take on any values between them. of light. E = 0, hυ, 2hυ , 3hυ....nhυ..... (iii)For each metal, there is a characteristic minimum frequency, ν (also known 0 as threshold frequency) below which photoelectric effect is not observed. At a frequency ν >ν , the ejected electrons come out with certain kinetic energy. The kinetic energies of these electrons increase with the increase of frequency of the light used. All the above results could not be explained on the basis of laws of classical physics. According to latter, the energy content of the Fig.2.9 Equipmentforstudyingthephotoelectric effect. Light of a particular frequency beam of light depends upon the brightness of strikes a clean metal surface inside a the light. In other words, number of electrons vacuum chamber. Electrons are ejected ejected and kinetic energy associated with from the metal and are counted by a them should depend on the brightness of light. detector that measures their kinetic energy. It has been observed that though the number Reprint 2026-27