Electronvolt

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Aerial photo of the Tevatron at Fermilab, which resembles a figure eight. The main accelerator is the ring above; the one below (about half the diameter, despite appearances) is for preliminary acceleration, beam cooling and storage, etc.

Particle accelerator

Machine that uses electromagnetic fields to propel charged particles to very high speeds and energies, and to contain them in well-defined beams.

Machine that uses electromagnetic fields to propel charged particles to very high speeds and energies, and to contain them in well-defined beams.

Aerial photo of the Tevatron at Fermilab, which resembles a figure eight. The main accelerator is the ring above; the one below (about half the diameter, despite appearances) is for preliminary acceleration, beam cooling and storage, etc.
Animation showing the operation of a linear accelerator, widely used in both physics research and cancer treatment.
Beamlines leading from the Van de Graaff accelerator to various experiments, in the basement of the Jussieu Campus in Paris.
Building covering the 2 mile (3.2 km) beam tube of the Stanford Linear Accelerator (SLAC) at Menlo Park, California, the second most powerful linac in the world.
A Cockcroft-Walton generator (Philips, 1937), residing in Science Museum (London).
A 1960s single stage 2 MeV linear Van de Graaff accelerator, here opened for maintenance
Modern superconducting radio frequency, multicell linear accelerator component.
Lawrence's 60 inch cyclotron, with magnet poles 60 inches (5 feet, 1.5 meters) in diameter, at the University of California Lawrence Radiation Laboratory, Berkeley, in August, 1939, the most powerful accelerator in the world at the time. Glenn T. Seaborg and Edwin McMillan (right) used it to discover plutonium, neptunium and many other transuranic elements and isotopes, for which they received the 1951 Nobel Prize in chemistry.
A magnet in the synchrocyclotron at the Orsay proton therapy center
Segment of an electron synchrotron at DESY
A Livingston chart depicting progress in collision energy through 2010. The LHC is the largest collision energy to date, but also represents the first break in the log-linear trend.

It is a collider accelerator, which can accelerate two beams of protons to an energy of 6.5 TeV and cause them to collide head-on, creating center-of-mass energies of 13 TeV.

Electric field of a positive and a negative point charge

Elementary charge

Electric charge carried by a single proton or, equivalently, the magnitude of the negative electric charge carried by a single electron, which has charge −1 e. This elementary charge is a fundamental physical constant.

Electric charge carried by a single proton or, equivalently, the magnitude of the negative electric charge carried by a single electron, which has charge −1 e. This elementary charge is a fundamental physical constant.

Electric field of a positive and a negative point charge

However, the unit of energy electronvolt reminds us that the elementary charge was once called electron.

A plasma lamp, using electrical energy to create plasma light, heat, movement and a faint sound

Joule

Derived unit of energy in the International System of Units.

Derived unit of energy in the International System of Units.

A plasma lamp, using electrical energy to create plasma light, heat, movement and a faint sound

Zeptojoule: The zeptojoule (zJ) is equal to one sextillionth of one joule. 160 zJ is about one electronvolt. The minimal energy needed to change a bit at around room temperature – approximately 2.75 zJ – is given by the Landauer limit.

A 2 kg cast iron weight used for balances

Mass

Quantity of matter in a physical body.

Quantity of matter in a physical body.

A 2 kg cast iron weight used for balances
The kilogram is one of the seven SI base units.
Depiction of early balance scales in the Papyrus of Hunefer (dated to the 19th dynasty, c. 1285 BCE). The scene shows Anubis weighing the heart of Hunefer.
Galileo Galilei (1636)
Distance traveled by a freely falling ball is proportional to the square of the elapsed time
Isaac Newton 1689
A cannon on top of a very high mountain shoots a cannonball horizontally. If the speed is low, the cannonball quickly falls back to Earth (A, B). At intermediate speeds, it will revolve around Earth along an elliptical orbit (C, D). Beyond the escape velocity, it will leave the Earth without returning (E).
An apple experiences gravitational fields directed towards every part of the Earth; however, the sum total of these many fields produces a single gravitational field directed towards the Earth's center
Vertical section drawing of Cavendish's torsion balance instrument including the building in which it was housed. The large balls were hung from a frame so they could be rotated into position next to the small balls by a pulley from outside. Figure 1 of Cavendish's paper.
Massmeter, a device for measuring the inertial mass of an astronaut in weightlessness. The mass is calculated via the oscillation period for a spring with the astronaut attached (Tsiolkovsky State Museum of the History of Cosmonautics)

the electronvolt (eV), a unit of energy, used to express mass in units of eV/c2 through mass–energy equivalence

The emission of electrons from a metal plate caused by light quanta – photons.

Photoelectric effect

Emission of electrons when electromagnetic radiation, such as light, hits a material.

Emission of electrons when electromagnetic radiation, such as light, hits a material.

The emission of electrons from a metal plate caused by light quanta – photons.
Schematic of the experiment to demonstrate the photoelectric effect. Filtered, monochromatic light of a certain wavelength strikes the emitting electrode (E) inside a vacuum tube. The collector electrode (C) is biased to a voltage VC that can be set to attract the emitted electrons, when positive, or prevent any of them from reaching the collector when negative.
Diagram of the maximum kinetic energy as a function of the frequency of light on zinc.
The gold leaf electroscope to demonstrate the photoelectric effect. When the electroscope is negatively charged, there is an excess of electrons and the leaves are separated. If short wavelength, high-frequency light (such as ultraviolet light obtained from an arc lamp, or by burning magnesium, or by using an induction coil between zinc or cadmium terminals to produce sparking) shines on the cap, the electroscope discharges, and the leaves fall limp. If, however, the frequency of the light waves is below the threshold value for the cap, the leaves will not discharge, no matter how long one shines the light at the cap.
Photomultiplier
Angle-resolved photoemission spectroscopy (ARPES) experiment. Helium discharge lamp shines ultraviolet light onto the sample in ultra-high vacuum. Hemispherical electron analyzer measures the distribution of ejected electrons with respect to energy and momentum.

Emission of conduction electrons from typical metals requires a few electron-volt (eV) light quanta, corresponding to short-wavelength visible or ultraviolet light.

The former Weights and Measures office in Seven Sisters, London

Unit of measurement

Definite magnitude of a quantity, defined and adopted by convention or by law, that is used as a standard for measurement of the same kind of quantity.

Definite magnitude of a quantity, defined and adopted by convention or by law, that is used as a standard for measurement of the same kind of quantity.

The former Weights and Measures office in Seven Sisters, London
Units of measurement, Palazzo della Ragione, Padua
An example of metrication in 1860 when Tuscany became part of modern Italy (ex. one "libbra" = 339.54 grams)

These may include the solar mass (2 kg), the megaton (the energy released by detonating one million tons of trinitrotoluene, TNT) and the electronvolt.

Artist's rendition of the Earth's plasma fountain, showing oxygen, helium, and hydrogen ions that gush into space from regions near the Earth's poles. The faint yellow area shown above the north pole represents gas lost from Earth into space; the green area is the aurora borealis, where plasma energy pours back into the atmosphere.

Plasma (physics)

One of the four fundamental states of matter.

One of the four fundamental states of matter.

Artist's rendition of the Earth's plasma fountain, showing oxygen, helium, and hydrogen ions that gush into space from regions near the Earth's poles. The faint yellow area shown above the north pole represents gas lost from Earth into space; the green area is the aurora borealis, where plasma energy pours back into the atmosphere.
Lightning as an example of plasma present at Earth's surface:
Typically, lightning discharges 30 kiloamperes at up to 100 megavolts, and emits radio waves, light, X- and even gamma rays. Plasma temperatures can approach 30000 K and electron densities may exceed 1024 m−3.
The complex self-constricting magnetic field lines and current paths in a field-aligned Birkeland current that can develop in a plasma.
Artificial plasma produced in air by a Jacob's Ladder
Cascade process of ionization. Electrons are "e−", neutral atoms "o", and cations "+".
Avalanche effect between two electrodes. The original ionization event liberates one electron, and each subsequent collision liberates a further electron, so two electrons emerge from each collision: the ionizing electron and the liberated electron.
Hall effect thruster. The electric field in a plasma double layer is so effective at accelerating ions that electric fields are used in ion drives.
Plasma spraying
Tokamak plasma in nuclear fusion research
Argon Plasma in the Hawkeye Linearly Magnetized Experiment (HLMX) at the University of Iowa

Plasma temperature, commonly measured in kelvin or electronvolts, is a measure of the thermal kinetic energy per particle.

Distance marker on the Rhine: 36 (XXXVI) myriametres from Basel. The stated distance is 360 km; the decimal mark in Germany is a comma.

Metric prefix

Unit prefix that precedes a basic unit of measure to indicate a multiple or submultiple of the unit.

Unit prefix that precedes a basic unit of measure to indicate a multiple or submultiple of the unit.

Distance marker on the Rhine: 36 (XXXVI) myriametres from Basel. The stated distance is 360 km; the decimal mark in Germany is a comma.

They are also used with other specialized units used in particular fields (e.g., megaelectronvolt, gigaparsec, millibarn).

Cloud chamber photograph by C. D. Anderson of the first positron ever identified. A 6 mm lead plate separates the chamber. The deflection and direction of the particle's ion trail indicate that the particle is a positron.

Positron

Antiparticle or the antimatter counterpart of the electron.

Antiparticle or the antimatter counterpart of the electron.

Cloud chamber photograph by C. D. Anderson of the first positron ever identified. A 6 mm lead plate separates the chamber. The deflection and direction of the particle's ion trail indicate that the particle is a positron.
Wilson cloud chambers used to be very important particle detectors in the early days of particle physics. They were used in the discovery of the positron, muon, and kaon.

These positrons soon find an electron, undergo annihilation, and produce pairs of 511 keV photons, in a process similar (but much lower intensity) to that which happens during a PET scan nuclear medicine procedure.

Countries using the metric (SI), imperial, and US customary systems as of 2019.

International System of Units

Modern form of the metric system and the world's most widely used system of measurement.

Modern form of the metric system and the world's most widely used system of measurement.

Countries using the metric (SI), imperial, and US customary systems as of 2019.
Arrangement of the principal measurements in physics based on the mathematical manipulation of length, time, and mass.
While not an SI-unit, the litre may be used with SI units. It is equivalent to (10 cm)3 = (1 dm)3 = 10−3 m3.
In the expression of acceleration due to gravity, a space separates the value and the units, both the 'm' and the 's' are lowercase because neither the metre nor the second are named after people, and exponentiation is represented with a superscript '2'.
Cover of brochure The International System of Units
Silicon sphere for the Avogadro project used for measuring the Avogadro constant to a relative standard uncertainty of 2 or less, held by Achim Leistner
Reverse dependencies of the SI base units on seven physical constants, which are assigned exact numerical values in the 2019 redefinition. Unlike in the previous definitions, the base units are all derived exclusively from constants of nature. Arrows are shown in the opposite direction compared to typical dependency graphs, i.e..
Stone marking the Austro-Hungarian/Italian border at Pontebba displaying myriametres, a unit of 10 km used in Central Europe in the 19th century (but since deprecated)
Closeup of the National Prototype Metre, serial number 27, allocated to the United States

Some common examples of such units are the customary units of time, namely the minute (conversion factor of 60 s/min, since 1 min = 60 s), the hour (3,600 s), and the day (86,400 s); the degree (for measuring plane angles, and the electronvolt (a unit of energy,