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The elementary charge, usually denoted by e, is a fundamental physical constant, defined as the electric charge carried by a single proton (+1 e) or, equivalently, the magnitude of the negative electric charge carried by a single electron, which has charge −1 e. [2] [a]
The law of conservation of charge always applies, giving the object from which a negative charge is taken a positive charge of the same magnitude, and vice versa. Even when an object's net charge is zero, the charge can be distributed non-uniformly in the object (e.g., due to an external electromagnetic field, or bound polar
The elementary charge e, i.e. the negative charge on a single electron or the positive charge on a single proton [3] 10 −18: atto-(aC) ~ 1.8755 × 10 −18 C: Planck charge [4] [5] 10 −17: 1.473 × 10 −17 C (92 e) – Positive charge on a uranium nucleus (derived: 92 x 1.602 × 10 −19 C) 10 −16: 1.344 × 10 −16 C: Charge on a dust ...
Within the limits of experimental accuracy, the electron charge is identical to the charge of a proton, but with the opposite sign. [83] The electron is commonly symbolized by e −, and the positron is symbolized by e +. [79] [80] The electron has an intrinsic angular momentum or spin of ħ / 2 . [80]
A proton by definition carries a charge of exactly 1.602 176 634 × 10 −19 coulombs. This value is also defined as the elementary charge . No object can have a charge smaller than the elementary charge, and any amount of charge an object may carry is a multiple of the elementary charge.
When charged particles move in electric and magnetic fields the following two laws apply: Lorentz force law: = (+),; Newton's second law of motion: = =; where F is the force applied to the ion, m is the mass of the particle, a is the acceleration, Q is the electric charge, E is the electric field, and v × B is the cross product of the ion's velocity and the magnetic flux density.
The coulomb was originally defined, using the latter definition of the ampere, as 1 A × 1 s. [4] The 2019 redefinition of the ampere and other SI base units fixed the numerical value of the elementary charge when expressed in coulombs and therefore fixed the value of the coulomb when expressed as a multiple of the fundamental charge.
e = elementary positive charge (i.e., magnitude of electron charge), m e = electron mass, k = Boltzmann constant = 1.38 × 10 −23 J/K, h = Planck constant = 6.62 × 10 −34 J⋅s, ϕ = work function of the cathode, ~ = mean electron reflection coefficient. The reflection coefficient can be as low as 0.105 but is usually near 0.5.