The very earliest models for electron spin imagined a rotating charged mass, but this model fails when examined in detail: the required space distribution does not match limits on the electron radius: the required rotation speed exceeds the speed of light. Often, the 'spin quantum number' is simply called 'spin'. In practice, spin is usually given as a dimensionless spin quantum number by dividing the spin angular momentum by the reduced Planck constant ħ, which has the same dimensions as angular momentum. The SI unit of spin is the same as classical angular momentum (i.e., N These are indicated by assigning the particle a spin quantum number. All elementary particles of a given kind have the same magnitude of spin angular momentum, though its direction may change. Spinors and bispinors behave similarly to vectors: they have definite magnitudes and change under rotations however, they use an unconventional 'direction'. Spin is described mathematically as a vector for some particles such as photons, and as spinors and bispinors for other particles such as electrons. The existence of the electron spin can also be inferred theoretically from the spin–statistics theorem and from the Pauli exclusion principle-and vice versa, given the particular spin of the electron, one may derive the Pauli exclusion principle. The existence of electron spin angular momentum is inferred from experiments, such as the Stern–Gerlach experiment, in which silver atoms were observed to possess two possible discrete angular momenta despite having no orbital angular momentum. : 183–184 Spin should not be understood as in the 'rotating internal mass' sense: spin is a quantized wave property. Spin is an intrinsic form of angular momentum carried by elementary particles, and thus by composite particles such as hadrons, atomic nuclei, and atoms. For the concept in classical mechanics, see Rotation. This article is about the concept in quantum mechanics. It is common to informally express mass in terms of eV as a unit of mass, effectively using a system of natural units with c set to 1.

It is common in particle physics, where units of mass and energy are often interchanged, to express mass in units of eV/ c 2, where c is the speed of light in vacuum (from E = mc 2). Relation to other physical properties and units Measurementīy mass–energy equivalence, the electronvolt corresponds to a unit of mass. The electronvolt (eV) is a unit of energy, but is not an SI unit. Therefore, one electronvolt is equal to 1.602 176 634 ×10 −19 J.

Hence, it has a value of one volt, 1 J/C, multiplied by the elementary charge e = 1.602 176 634 ×10 −19 C. In some older documents, and in the name Bevatron, the symbol BeV is used, which stands for billion (10 9) electronvolts it is equivalent to the GeV.Īn electronvolt is the amount of kinetic energy gained or lost by a single electron accelerating from rest through an electric potential difference of one volt in vacuum. It is commonly used with SI prefixes milli-, kilo-, mega-, giga-, tera-, peta- or exa- (meV, keV, MeV, GeV, TeV, PeV and EeV respectively). It is a common unit of energy within physics, widely used in solid state, atomic, nuclear, and particle physics, and high-energy astrophysics. Since q must be an integer multiple of the elementary charge e for any isolated particle, the gained energy in units of electronvolts conveniently equals that integer times the voltage. Historically, the electronvolt was devised as a standard unit of measure through its usefulness in electrostatic particle accelerator sciences, because a particle with electric charge q gains an energy E = qV after passing through a voltage of V.

Under the 2019 redefinition of the SI base units, this sets 1 eV equal to the exact value 1.602 176 634 ×10 −19 J. When used as a unit of energy, the numerical value of 1 eV in joules (symbol J) is equivalent to the numerical value of the charge of an electron in coulombs (symbol C). In physics, an electronvolt (symbol eV, also written electron-volt and electron volt) is the measure of an amount of kinetic energy gained by a single electron accelerating from rest through an electric potential difference of one volt in vacuum. For other uses, see MEV, KEV, GEV, TEV and PEV. 'meV', 'keV', 'MeV', 'GeV', 'TeV' and 'PeV' redirect here.

Standard charge of electron