Elektron - Wikipedia

# Elektron

### From Wikipedia

  Untuk kegunaan yang lain, sila lihat: Elektron (nyahkekaburan).

Elektron
Beberapa atom hydrogen orbital electron ditunjukkan pada keratan rentas dengan berketumpatan kebarangkalian berkod warna
Klasifikasi

Partikel Zarah
Fermion
Lepton
Generasi Pertama
Elektron

Ciri-ciri

Mass: | 9.109 3826(16) × 10−31 kg
| 1⁄1836.152 672 61(85) uja |
| 0.510 998 918(44) MeV/c2
Cas Elektrik: | −1.602 176 53(14) × 10−19 C
Putaran: | ½
Cas Warna: | tiada
Interaksi: | Graviti, Elektromagnetik, Lemah

Elektron adalah satu zarah subatom asas berjisim ringan yang membawa cas negatif cas elektrik. Electron mempunyai putaran-1/2 lepton, tidak terlibat didalam interaksi kuat dan tidak mempunyai substruktur. Bersama-sama dengan nucleus atom , elektron membina atom-atom; mereka bertanggungjawab kepada ikatan kimia. Pengaliran elektrik dalam pengalir(konduktor) pepejal adalah disebabkan pergerakan elektron-elektron.

## [Sunting] Pendahuluan

Dalam sesuatu atom, elektron mengelilingi nukleus atom bagi proton dan neutron dalam tatarajah elektron. Perkataan elektron yang dicipta pada tahun 1894 berasal daripada istilah daya elektrik yang diperkenalkan oleh William Gilbert. Asalnya ialah ήλεκτρον (elektron), sepatah perkataan Greek yang membawa maksud ambar.

Elektron-elektron yang bergerak menghasilkan arus elektrik yang boleh dipergunakan oleh ahli-ahli sains dan jurutera-jurutera untuk mengukur banyak sifat fizik. Arus elektrik wujud untuk tempoh yang terbatas dan menghasilkan elektrik (pergerakan cas) yang boleh dimanfaatkan sebagai cara yang praktik untuk melakukan kerja.

Pemahamanan tentang elektron-elektron telah berubah secara dramatik sejak beberapa abad yang lalu, dengan perubahan yang paling penting mungkin merupakan perkembangan mekanik kuantum pada abad ke-20 dan idea kembaran zarah gelombang, iaitu elektron menampilkan kedua-dua sifat zarah dan gelombang. Yang serupa penting, fizik zarah telah meluaskan pemahaman kita terhadap elektron secara tidak terhingga.

Perubahan-perubahan dalam medan elektrik yang dijanakan oleh bilangan-bilangan elektron yang berbeza dan tatarajah-tatarajah atomnya menentukan sifat kimia unsur-unsur. Medan-medan ini memainkan peranan yang asas dalam ikatan-ikatan kimia dan kimia.

## [Sunting] Secara praktis

### [Sunting] Pengelasan

Elektron merupakan salah satu kelas zarah subatom yang dipanggil sebagai lepton. Lepton dipercayai merupakan zarah asas, iaitu zarah ini tidak boleh dipecahkan lagi menjadi unsur-unsur juzuk. Bagaimanapun, istilah "zarah" adalah agak mengelirukan kerana mekanik kuantum menunjukkan bahawa elektron-elektron juga bertindak sebagai gelombang, umpamanya dalam uji kaji celah ganda dua; ini dipanggil sebagai kembaran zarah gelombang.

Antizarah untuk elektron ialah positron yang mempunyai jisim yang sama, tetapi mempunyai cas positif dan bukannya cas negatif. Carl D. Anderson, penemu positron, mencadangkan nama negatron untuk elektron piawai, dan nama elektron sebagai istilah generik untuk memerihalkan kedua-dua kelainan cas positif serta cas negatif. Bagaimanapun, kegunaan istilah ini tidak mendapat sambutan, dan amat jarang ditemukan pada hari ini.

Rencana ini diterjemahkan daripada sebahagian rencana Wikipedia bahasa Inggeris. Bantulah Wikipedia menterjemahkan lagi seperenggan dua. Bahan-bahan boleh didapati di en:Elektron. |
Terima kasih kerana membaca rencana ini. Sumber bantuan: Kamus Dewan Bahasa

### [Sunting] Ciri-ciri dan kelakuan

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−.

According to quantum mechanics, electrons can be represented by wavefunctions, from which the electron density can be determined. Each electron has its own wavefunction, which is called an orbital. 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.

The electron has spin ½ and is a fermion (it obeys Fermi-Dirac statistics). In addition to its intrinsic angular momentum, an electron has a magnetic moment along its spin axis.

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 an electric current.

A body has a static charge when the body 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, their charges cancel each other and the object is said to be electrically neutral. A macroscopic body can acquire charge through rubbing, by the phenomenon of triboelectricity. Electrons and positrons can annihilate each other and produce a pair of photons. However, high-energy photons may transform into an electron and a positron by a process called pair production.

The electron is an elementary particle — it has no substructure (at least, experiments have found none so far, and there is good reason to think that there is none). Hence, it is usually described as point-like, 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).

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).

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:

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:

  = 0.999 999 999 95 c.

(The formula applies for large γ.)

### [Sunting] Di dalam alam semesta

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.

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.

### [Sunting] Di dalam industri

Electron beams are used in welding as well as lithography.

## [Sunting] Di dalam makmal

### [Sunting] Eksperimen awal

The quantum or discrete nature of electron's charge was observed by Robert Millikan in the Oil-drop experiment of 1909.

### [Sunting] Penggunaan

Electron microscopes are used to magnify details up to 500,000 times. Quantum effects of electrons are used in Scanning tunneling microscope to study features at the atomic scale.

## [Sunting] Secara teori

In relativistic quantum mechanics, the electron is described by the Dirac Equation. Quantum electrodynamics (QED) models an electron as a charged particle surrounded by a sea of interacting virtual particles, modifying the sea of virtual particles which makes up a vacuum. Although this theory involves difficult theoretical problems where calculations produce infinite terms, a practical (although mathematically dubious) method called renormalization was discovered whereby infinite terms can be cancelled to produce finite predictions about the electron. The correction of just over 0.1% to the predicted value of the electron's gyromagnetic ratio from exactly 2 (as predicted by Dirac's single particle model), and its extraordinarily precise agreement with the experimentally determined value, is viewed as one of the pinnacles of modern physics. There are now indications that string theory and its descendants may provide a model of the electron and other fundamental particles where the infinities in calculations do not appear, because the electron is no longer seen as a dimensionless point. At present, string theory is very much a 'work in progress' and lacks predictions analogous to those made by QED that can be experimentally verified.

In the Standard Model of particle physics, it forms a doublet in SU(2) with the electron neutrino, as they interact through the weak interaction. The electron has two more massive partners, with the same charge but different masses: the muon and the tau lepton.

The antimatter counterpart of the electron is its antiparticle, the positron. The positron has the same amount of electrical charge as the electron, except that the charge is positive. It has the same mass and spin as the electron. When an electron and a positron meet, they may annihilate each other, giving rise to two gamma-ray photons, each having an energy of 0.511 MeV (511 keV). See also Electron-positron annihilation.

Electrons are also a key element in electromagnetism, an approximate theory that is adequate for macroscopic systems, and for classical modelling of microscopic systems.

## [Sunting] Sejarah

The electron as a unit of charge in electrochemistry was posited by G. Johnstone Stoney in 1874, who also coined usage of "electron" in 1894. During the late 1890s a number of physicists posited that electricity could be conceived of as being made of discrete units, which were given a variety of names, but their reality had not been confirmed in a compelling way.

The discovery that the electron was a subatomic particle was made in 1897 by J.J. Thomson at the Cavendish Laboratory at Cambridge University, while he was studying "cathode rays". Influenced by the work of James Clerk Maxwell, and the discovery of the X-ray, he deduced that cathode rays existed and were negatively charged "particles", which he called "corpuscles." He published his discovery in 1897.

The periodic law states that the chemical properties of elements largely repeat themselves periodically and is the foundation of the periodic table of elements. The law itself was initially explained by the atomic mass of the elements. However, as there were anomalies in the periodic table, efforts were made to find a better explanation for it. In 1913, Henry Moseley introduced the concept of the atomic number and explained the periodic law with the number of protons each element has. In the same year, Niels Bohr showed that electrons are the actual foundation of the table. In 1916, Gilbert Newton Lewis explained the chemical bonding of elements by electronic interactions.

## [Sunting] Lihat juga

- Standard Model
- Subatomic particle
- Proton
- Positron
- Neutron
- Photoelectric effect
- Lightning
- List of particles
- Cathode rays
- Electricity
- Fermion field

## [Sunting] Rujukan

- Griffiths, David J. (2004). Introduction to Quantum Mechanics (2nd ed.), Prentice Hall. ISBN 013805326X.
- Tipler, Paul; Llewellyn, Ralph (2002). Modern Physics (4th ed.), W. H. Freeman. ISBN 0716743450.
- Brumfiel, G. (6 January 2005). Can electrons do the splits? In Nature, 433, 11.

## [Sunting] Pautan luar

Wikisource mempunyai sumber asli 1911 Encyclopædia Britannica teks berkaitan kepada:
Elektron

- The Discovery of the Electron from the American Institute of Physics History Center
- Particle Data Group
- Stoney, G. Johnstone, "Of the 'Electron,' or Atom of Electricity". Philosophical Magazine. Series 5, Volume 38, p. 418-420 October 1894.
- Eric Weisstein's World of Physics: Electron

Zarah dalam fizik - Zarah-zarah unsur | edit
Fermions: Quark | Lepton
Quarks: Up | Down | Strange | Charm | Bottom | Top
Lepton: Elektron | Muon | Tau | Neutrinos
Gauge boson: Foton | W and Z boson | Gluons
Not yet observed: Higgs boson | Graviton | Other hypothetical particles

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