Elementary charge – wikipedia gas leak los angeles california


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. [5] 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.

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.)

• Quarks, first posited in the 1960s, have quantized charge, but the charge is quantized into multiples of 1 / 3 e. However, quarks cannot be seen as isolated particles; they exist only in groupings, and stable groupings of quarks (such as a proton, which consists of three quarks) all have charges that are integer multiples of e. For this reason, either 1 e or 1 / 3 e can be justifiably considered to be "the quantum of charge", depending on the context. This charge commensurability, "charge quantization", has partially motivated Grand unified Theories.

• Quasiparticles are not particles as such, but rather an emergent entity in a complex material system that behaves like a particle. In 1982 Robert Laughlin explained the fractional quantum Hall effect by postulating the existence of fractionally-charged quasiparticles. This theory is now widely accepted, but this is not considered to be a violation of the principle of charge quantization, since quasiparticles are not elementary particles.

All known elementary particles, including quarks, have charges that are integer multiples of 1 / 3 e. Therefore, one can say that the " quantum of charge" is 1 / 3 e. In this case, one says that the "elementary charge" is three times as large as the "quantum of charge".

On the other hand, all isolatable particles have charges that are integer multiples of e. (Quarks cannot be isolated: they only exist in collective states like protons that have total charges that are integer multiples of e.) Therefore, one can say that the "quantum of charge" is e, with the proviso that quarks are not to be included. In this case, "elementary charge" would be synonymous with the "quantum of charge".

In fact, both terminologies are used. [7] For this reason, phrases like "the quantum of charge" or "the indivisible unit of charge" can be ambiguous, unless further specification is given. On the other hand, the term "elementary charge" is unambiguous: it universally refers to a quantity of charge equal to that of a proton.

The value of the Avogadro constant N A was first approximated by Johann Josef Loschmidt who, in 1865, estimated the average diameter of the molecules in air by a method that is equivalent to calculating the number of particles in a given volume of gas. [8] Today the value of N A can be measured at very high accuracy by taking an extremely pure crystal (in practice, often silicon), measuring how far apart the atoms are spaced using X-ray diffraction or another method, and accurately measuring the density of the crystal. From this information, one can deduce the mass ( m) of a single atom; and since the molar mass ( M) is known, the number of atoms in a mole can be calculated: N A = M/ m. [9]

The value of F can be measured directly using Faraday’s laws of electrolysis. Faraday’s laws of electrolysis are quantitative relationships based on the electrochemical researches published by Michael Faraday in 1834. [10] In an electrolysis experiment, there is a one-to-one correspondence between the electrons passing through the anode-to-cathode wire and the ions that plate onto or off of the anode or cathode. Measuring the mass change of the anode or cathode, and the total charge passing through the wire (which can be measured as the time-integral of electric current), and also taking into account the molar mass of the ions, one can deduce F. [9]

The limit to the precision of the method is the measurement of F: the best experimental value has a relative uncertainty of 1.6 ppm, about thirty times higher than other modern methods of measuring or calculating the elementary charge. [9] [11] Oil-drop experiment [ edit ]

Any electric current will be associated with noise from a variety of sources, one of which is shot noise. Shot noise exists because a current is not a smooth continual flow; instead, a current is made up of discrete electrons that pass by one at a time. By carefully analyzing the noise of a current, the charge of an electron can be calculated. This method, first proposed by Walter H. Schottky, can determine a value of e of which the accuracy is limited to a few percent. [12] However, it was used in the first direct observation of Laughlin quasiparticles, implicated in the fractional quantum Hall effect. [13] From the Josephson and von Klitzing constants [ edit ]

Another accurate method for measuring the elementary charge is by inferring it from measurements of two effects in quantum mechanics: The Josephson effect, voltage oscillations that arise in certain superconducting structures; and the quantum Hall effect, a quantum effect of electrons at low temperatures, strong magnetic fields, and confinement into two dimensions. The Josephson constant is K J = 2 e h {\displaystyle K_{\mathrm {J} }={\frac {2e}{h}}}

In the most recent CODATA adjustments, [9] the elementary charge is not an independently defined quantity. [14] Instead, a value is derived from the relation e 2 = 2 h α μ 0 c = 2 h α ϵ 0 c {\displaystyle e^{2}={\frac {2h\alpha }{\mu _{0}c}}=2h\alpha \epsilon _{0}c}

where h is the Planck constant, α is the fine-structure constant, μ 0 is the magnetic constant, ε 0 is the electric constant and c is the speed of light. The uncertainty in the value of e is currently determined almost entirely by the uncertainty in the Planck constant.