Electron

Electrons in practice

Classification of electrons

The electron is one of a class of subatomic particles called leptons which are believed to be fundamental particles (that is, they cannot be broken down into smaller constituent parts). The word "particle" is somewhat misleading however, because quantum mechanics shows that electrons also behave like a wave, e.g. in the double-slit experiment; this is called wave-particle duality.

Related Topics:
Lepton - Fundamental particles - Quantum mechanics - Double-slit experiment - Wave-particle duality

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The antiparticle of an electron is the positron, which has the same mass but positive rather than negative charge. The term negatron is sometimes used to refer to standard electrons so that the term electron may be used to describe both positrons and negatrons, as proposed by Carl D. Anderson. Under ordinary circumstances, however, electron refers to the negatively charged particle alone.

Related Topics:
Positron - Carl D. Anderson

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Properties and behavior of electrons

Electrons have a negative electric charge of −1.6 × 10−19 coulombs, and a mass of about 9.11 × 10−31 kg (0.51 MeV/c2), which is approximately 1⁄1836 of the mass of the proton. These are commonly represented as e−.

Related Topics:
Electric charge - Coulomb - 9.11 × 10⁻³¹ kg - Proton

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According to quantum mechanics, electrons can be represented by wavefunctions, from which the electron density can be determined. The exact momentum and position of an electron cannot be simultaneously determined. This is a limitation described by the Heisenberg uncertainty principle, which, in this instance, simply states that the more accurately we know a particle's position, the less accurately we can know its momentum and vice versa.

Related Topics:
Quantum mechanics - Wavefunction - Electron density - Heisenberg uncertainty principle

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The electron has spin ½, which implies it is a fermion, i.e., it follows the Fermi-Dirac statistics. While most electrons are found in atoms, others move independently in matter, or together as an electron beam in a vacuum. In some superconductors, electrons move in Cooper pairs, in which their motion is coupled to nearby matter via lattice vibrations called phonons. When electrons move, free of the nuclei of atoms, and there is a net flow, this flow is called electricity, or an electric current.

Related Topics:
Spin - Fermion - Fermi-Dirac statistics - Electron beam - Vacuum - Superconductor - Electricity - Electric current

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A body has a static charge, when the body that has more or fewer electrons than are required to balance the positive charge of the nuclei. When there is an excess of electrons, the object is said to be negatively charged. When there are fewer electrons than protons, the object is said to be positively charged. When the number of electrons and the number of protons are equal, the object is said to be electrically neutral. A macroscopic body can aquire charge through rubbing, i.e. the phenomena pf triboelectricity. Electrons and positrons can annihilate each other and produce a pair of photons. Conversely, a high-energy photon can be transformed into an electron and a positron by a process called pair production.

Related Topics:
Proton - Triboelectricity - Positron - Annihilate - Photons - Pair production

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The electron is an elementary particle— that means that it has no substructure (at least, experiments have not found any so far, and there is good reason to believe that there is not any). Hence, it is usually described as point-like, i.e. with no spatial extension. However, if one gets very near an electron, one notices that its properties (charge and mass) seem to change. This is an effect common to all elementary particles: the particle influences the vacuum fluctuations in its vicinity, so that the properties one observes from far away are the sum of the bare properties and the vacuum effects (see renormalization).

Related Topics:
Elementary particle - Substructure - Point - Charge - Mass - Vacuum fluctuation - Renormalization

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There is a physical constant called the classical electron radius, with a value of 2.8179 × 10−15 m. Note that this is the radius that one could infer from its charge if the physics were only described by the classical theory of electrodynamics and there were no quantum mechanics (hence, it is an outdated concept that nevertheless sometimes still proves useful in calculations).

Related Topics:
Classical electron radius - M - Classical - Electrodynamics - Quantum mechanics

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The speed of an electron in a vacuum can approach, but never reach c, the speed of light in a vacuum. This is due to an effect of special relativity. The effects of special relativity are based on a quantity known as gamma or the Lorentz factor. Gamma is a function of v, the velocity of the particle, and c. The following is the formula for gamma:

Related Topics:
Vacuum - Speed of light - Special relativity - Lorentz factor

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:gamma = 1 / sqrt{1 - (v^2/c^2)}

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The energy necessary to accelerate a particle is gamma minus one times the rest mass. For example, the linear accelerator at Stanford can accelerate an electron to roughly 51 GeV. This gives you a gamma of 100,000 given that the rest mass of an electron is 0.51 MeV/c² (the relativistic mass of this fast electron is 100 000 times its rest mass). Solving the equation above for the speed of the electron gives a speed of:

Related Topics:
Linear accelerator - Stanford - Relativistic mass

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:(1-rac {1} {2} gamma ^{-2})c = 0.999 999 999 95 c.

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(The formula applies for large γ.)

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Electrons in the universe

It is believed that the number of electrons existing in the known universe is at least 1079. This number amounts to a density of about one electron per cubic metre of space.

Related Topics:
Universe - Cubic metre

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Based on the classical electron radius and assuming a dense sphere packing, it can be calculated that the number of electrons that would fit in the observable universe is on the order of 10130. Of course, this number is even less meaningful than the classical electron radius itself.

Related Topics:
Classical electron radius - Sphere packing - Observable universe

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Electrons in industry

Electron beams are used in welding as well as lithography.

Related Topics:
Electron beam - Welding - Lithography

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