7. PERMUTATIONS AND COMBINATIONS
Important Points
PARTICLE NATURE OF ELECTROMAGNETIC RADIATION: PHOTO ELECTRIC EFFECT
Particle Nature of Electromagnetic Radiation: Planck’s Quantum Theory The important postulates of quantum theory proposed by Max Planck are: 1. Atoms and molecules could emit or absorb energy not in a continuous manner, but discontinuously in small packets of energy called quanta or photons. 2. The energy (E ) of each quantum of radiation is proportional to its frequency (ν). It is expressed by the equation, E = hν Where ‘h’ is known as Planck’s constant and its value is 6.626×10–34 J s. Photoelectric effect It is the phenomenon of ejection of electrons by certain metals (like potassium, rubidium, caesium etc.) when light of suitable frequency incident on them. The electrons ejected are called photoelectrons. This phenomenon was first observed by H Hertz. The important characteristics of photoelectric effect are: 1. The electrons are ejected from the metal surface as soon as the beam of light strikes the surface. i.e., there is no time lag between the...
