Elementary charge

The elementary charge, usually denoted by e or sometimes qe, is the electric charge carried by a single proton or, equivalently, the magnitude of the electric charge carried by a single electron, which has charge −1 e. This elementary charge is a fundamental physical constant. To avoid confusion over its sign, e is sometimes called the elementary positive charge. The elementary charge, usually denoted by e or sometimes qe, is the electric charge carried by a single proton or, equivalently, the magnitude of the electric charge carried by a single electron, which has charge −1 e. This elementary charge is a fundamental physical constant. To avoid confusion over its sign, e is sometimes called the elementary positive charge. From the 2019 redefinition of SI base units, that took effect on 20 May 2019, its value is exactly 1.602176634×10−19 C by definition of the coulomb. In the centimetre–gram–second system of units (CGS), it is 4.80320425(10)×10−10 statcoulombs. Making the value of the elementary charge exact implies that the value of ε0 (electric constant), which was an exact value before, is now subject to experimental determination: ε0 had an exactly defined value until the 2019 SI redefinition, after which it has become a subject of experimental refinement with time. The SI committees(CGPM, CIPM, etc.) had long considered redefining the SI units entirely in terms of physical constants so as to remove their dependence on physical artifacts(such as the IPK): for this to work, it was necessary to fix the values of the physical constants. Robert A. Millikan's oil drop experiment first measured the magnitude of the elementary charge in 1909. In some natural unit systems, such as the system of atomic units, e functions as the unit of electric charge, that is e is equal to 1 e in those unit systems. The use of elementary charge as a unit was promoted by George Johnstone Stoney in 1874 for the first system of natural units, called Stoney units. Later, he proposed the name electron for this unit. At the time, the particle we now call the electron was not yet discovered and the difference between the particle electron and the unit of charge electron was still blurred. Later, the name electron was assigned to the particle and the unit of charge e lost its name. However, the unit of energy electronvolt reminds us that the elementary charge was once called electron. In high-energy physics (HEP), Lorentz–Heaviside units are used, and the charge unit is a dependent one, ℏ c {displaystyle {sqrt {hbar c}}} , so that e = √ 4 π α √ħc ≈ 0.30282212088 √ħc. Charge quantization is the principle that the charge of any object is an integer multiple of the elementary charge. Thus, an object's charge can be exactly 0 e, or exactly 1 e, −1 e, 2 e, etc., but not, say, 1/2 e, or −3.8 e, etc. (There may be exceptions to this statement, depending on how 'object' is defined; see below.)