This effect is observed when light focused on certain metals emits electrons. On the basis of these studies, Planck postulated a theory known as Planck’s quantum theory of radiations. Hence only certain orbits whose radii are given by the above equation are available for the electron. The wave model cannot account for something known as the photoelectric effect. Bohr developed a model for the hydrogen atom and hydrogen-like one-electron species (hydrogenic species). (iii) The energy of a quantum is directly proportional to the frequency of the radiation. where n is the positive integer. (iv) These rays do not require any medium for propagation. Such a stable state of the atom is called a ground state or normal state. In case of light the quantum is known as photon. Summary The agreement between Planck’s theory and the experimental observation provided strong evidence that the energy of electron motion in matter is quantized. In case of light, a quantum of light is known as a photon. Hence these orbits are called stationary state. Meanwhile, the energy of radiation is expressed in terms of frequency as, E = h ν. (iv) A body can radiate or absorb energy in whole number multiples of a quantum hv, 2hν, 3hν ….. nhν. CC BY-SA 3.0. http://commons.wikimedia.org/wiki/File:Nitrogen.Spectrum.Vis.jpg According to Bohr’s postulate of angular momentum quantization, we have. E depends upon v (nu). When the electrons return to the ground state, they emit energy of various wavelengths. Instead, there are discrete lines created by different wavelengths. Most importantly, this perspective points to a possible ex- tension of QM along the line discussed in , one relevant to a background independent The photoelectric effect could not be rationalized based on existing theories of light, as an increase in the intensity of light did not lead to the same outcome as an increase in the energy of the light. it is radiated in form of energy packets. http://en.wiktionary.org/wiki/electromagnetic_radiation, http://en.wikipedia.org/wiki/Planck_constant, http://www.boundless.com//physics/definition/photoelectric-effect, http://en.wikipedia.org/wiki/Quantum_mechanics, http://en.wikibooks.org/wiki/General_Chemistry/Introduction_to_Quantum_Theory, http://commons.wikimedia.org/wiki/File:Nitrogen.Spectrum.Vis.jpg, http://commons.wikimedia.org/wiki/File:Wavelength.png, https://www.boundless.com/chemistry/textbooks/boundless-chemistry-textbook/, Calculate the energy element E=hv, using Planck’s Quantum Theory. This observation led to the discovery of the minimum amount of energy that could be gained or lost by an atom. This began with Planck's formula for explaining the continuous spectrum of light radiation from heated solids. CC BY-SA 3.0. http://www.boundless.com//physics/definition/photoelectric-effect Wikimedia Frequency is the number of waves that pass by a given point each second. But if the energy supplied to a hydrogen atom is more than 13.6 eV then all photons are absorbed and excess energy appears as kinetic energy of emitted photo electrons. Wikipedia (iii) All the electromagnetic waves travel with the velocity of light. He applied quantum theory in considering the energy of an electron bound to the nucleus. The wavelength or frequency of any specific occurrence of EM radiation determine its position on the electromagnetic spectrum and can be calculated from the following equation: where c is the constant 3.0 x 108 m/sec (the speed of light in a vacuum), [latex]\lambda[/latex] = wavelength in meters, and [latex]\nu[/latex]=frequency in hertz (1/s). In some ways, quantum mechanics completely changed the way physicists viewed the universe, and it also marked the end of the idea of a clockwork universe (the idea that universe was predictable). According to Planck: E=h [latex]\nu [/latex], where h is Planck’s constant (6.62606957 (29) x 10 -34 J s), ν is the frequency, and E is energy of an electromagnetic wave.