In physics, a quantum is the minimum amount of any physical entity involved in an interaction. The fundamental notion that a physical property can be "quantized" is referred to as "the hypothesis of quantization". This means that the magnitude of the physical property can take on only values consisting of integer multiples of one quantum. For example, a photon is a single quantum of light. Similarly, the energy of an electronbound within an atom is quantized and can exist only in certain discrete values. Quantization is one of the foundations of the much broader physics of quantum mechanics. Quantization of energy and its influence on how energy and matter interact is part of the fundamental framework for understanding and describing nature.
Etymology and discovery
The word quantum is the neuter singular of the Latin interrogative adjective quantus, meaning "how much". "Quanta", the neuter plural, short for "quanta of electricity", was used in a 1902 article on the photoelectric effect by Philipp Lenard, who creditedHermann von Helmholtz for using the word in the area of electricity. However, the word quantum in general was well known before 1900. It was often used by physicians, such as in the term quantum satis. Both Helmholtz and Julius von Mayer were physicians as well as physicists. Helmholtz used quantum with reference to heat in his article on Mayer's work, and the word quantum can be found in the formulation of the first law of thermodynamics by Mayer in his letter dated July 24, 1841. In 1901, Max Planck used quanta to mean "quanta of matter and electricity", gas, and heat. In 1905, in response to Planck's work and the experimental work of Lenard, Albert Einstein suggested that radiation existed in spatially localized packets which he called "quanta of light". The concept of quantization of radiation was discovered in 1900 by Max Planck, who had been trying to understand the emission of radiation from heated objects, known as black-body radiation. By assuming that energy can be absorbed or released only in tiny, differential, discrete packets, Planck accounted for certain objects changing colour when heated. On December 14, 1900, Planck reported his findings to the German Physical Society, and introduced the idea of quantization for the first time as a part of his research on black-body radiation. As a result of his experiments, Planck deduced the numerical value of h, known as the Planck constant, and reported more precise values for the unit of electrical charge and the Avogadro-Loschmidt number, the number of real molecules in a mole, to the German Physical Society. After his theory was validated, Planck was awarded the Nobel Prize in Physics for his discovery in 1918.
Quantization
While quantization was first discovered in electromagnetic radiation, it describes a fundamental aspect of energy not just restricted to photons. In the attempt to bring theory into agreement with experiment, Max Planck postulated that electromagnetic energy is absorbed or emitted in discrete packets, or quanta.
