60 relations: Atom, Atomic nucleus, Attenuation, Attenuation coefficient, Attenuation length, Bar (unit), Beer–Lambert law, Boltzmann constant, Cross section (physics), Density, E (mathematical constant), Effective mass (solid-state physics), Electrical mobility, Electrical resistivity and conductivity, Electron, Elementary charge, Expected value, Fermi energy, Frequency distribution, Gamma ray, Half-value layer, Ideal gas law, Kinetic diameter, Kinetic theory of gases, Knudsen number, Lennard-Jones potential, Mach number, Mass attenuation coefficient, Maxwell–Boltzmann distribution, Mean, Mean free time, Micrometre, Mie scattering, Millimeter of mercury, Molecule, Nanometre, National Institute of Standards and Technology, Nucleon, Optics, Ordinary differential equation, Pair production, Pascal (unit), Pencil (optics), Photon, Physics, Pressure, Radiation length, Radiography, Reverberation, Scattering theory, ..., Spectrum, Springer Science+Business Media, Thin film, Torr, Transmittance, Vacuum, Victor Weisskopf, Viscosity, Volume fraction, X-ray. Expand index (10 more) »

## Atom

An atom is the smallest constituent unit of ordinary matter that has the properties of a chemical element.

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## Atomic nucleus

The atomic nucleus is the small, dense region consisting of protons and neutrons at the center of an atom, discovered in 1911 by Ernest Rutherford based on the 1909 Geiger–Marsden gold foil experiment.

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## Attenuation

In physics, attenuation or, in some contexts, extinction is the gradual loss of flux intensity through a medium.

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## Attenuation coefficient

Attenuation coefficient or narrow beam attenuation coefficient of the volume of a material characterizes how easily it can be penetrated by a beam of light, sound, particles, or other energy or matter.

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## Attenuation length

In physics, the attenuation length or absorption length is the distance \lambda into a material when the probability has dropped to 1/e that a particle has not been absorbed.

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## Bar (unit)

The bar is a metric unit of pressure, but is not approved as part of the International System of Units (SI).

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## Beer–Lambert law

The Beer–Lambert law, also known as Beer's law, the Lambert–Beer law, or the Beer–Lambert–Bouguer law relates the attenuation of light to the properties of the material through which the light is travelling.

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## Boltzmann constant

The Boltzmann constant, which is named after Ludwig Boltzmann, is a physical constant relating the average kinetic energy of particles in a gas with the temperature of the gas.

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## Cross section (physics)

When two particles interact, their mutual cross section is the area transverse to their relative motion within which they must meet in order to scatter from each other.

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## Density

The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume.

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## E (mathematical constant)

The number is a mathematical constant, approximately equal to 2.71828, which appears in many different settings throughout mathematics.

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## Effective mass (solid-state physics)

In solid state physics, a particle's effective mass (often denoted) is the mass that it seems to have when responding to forces, or the mass that it seems to have when interacting with other identical particles in a thermal distribution.

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## Electrical mobility

Electrical mobility is the ability of charged particles (such as electrons or protons) to move through a medium in response to an electric field that is pulling them.

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## Electrical resistivity and conductivity

Electrical resistivity (also known as resistivity, specific electrical resistance, or volume resistivity) is a fundamental property that quantifies how strongly a given material opposes the flow of electric current.

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## Electron

The electron is a subatomic particle, symbol or, whose electric charge is negative one elementary charge.

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## Elementary charge

The elementary charge, usually denoted as or sometimes, is the electric charge carried by a single proton, or equivalently, the magnitude of the electric charge carried by a single electron, which has charge.

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## Expected value

In probability theory, the expected value of a random variable, intuitively, is the long-run average value of repetitions of the experiment it represents.

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## Fermi energy

The Fermi energy is a concept in quantum mechanics usually referring to the energy difference between the highest and lowest occupied single-particle states in a quantum system of non-interacting fermions at absolute zero temperature.

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## Frequency distribution

In statistics, a frequency distribution is a list, table or graph that displays the frequency of various outcomes in a sample.

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## Gamma ray

A gamma ray or gamma radiation (symbol γ or \gamma), is penetrating electromagnetic radiation arising from the radioactive decay of atomic nuclei.

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## Half-value layer

A material's half-value layer (HVL), or half-value thickness, is the thickness of the material at which the intensity of radiation entering it is reduced by one half.

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## Ideal gas law

The ideal gas law, also called the general gas equation, is the equation of state of a hypothetical ideal gas.

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## Kinetic diameter

Kinetic diameter is a measure applied to atoms and molecules that expresses the likelihood that a molecule in a gas will collide with another molecule.

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## Kinetic theory of gases

The kinetic theory describes a gas as a large number of submicroscopic particles (atoms or molecules), all of which are in constant rapid motion that has randomness arising from their many collisions with each other and with the walls of the container.

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## Knudsen number

The Knudsen number (Kn) is a dimensionless number defined as the ratio of the molecular mean free path length to a representative physical length scale.

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## Lennard-Jones potential

The Lennard-Jones potential (also termed the L-J potential, 6-12 potential, or 12-6 potential) is a mathematically simple model that approximates the interaction between a pair of neutral atoms or molecules.

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## Mach number

In fluid dynamics, the Mach number (M or Ma) is a dimensionless quantity representing the ratio of flow velocity past a boundary to the local speed of sound.

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## Mass attenuation coefficient

The mass attenuation coefficient, mass extinction coefficient, or mass narrow beam attenuation coefficient of the volume of a material characterizes how easily it can be penetrated by a beam of light, sound, particles, or other energy or matter.

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## Maxwell–Boltzmann distribution

In physics (in particular in statistical mechanics), the Maxwell–Boltzmann distribution is a particular probability distribution named after James Clerk Maxwell and Ludwig Boltzmann.

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## Mean

In mathematics, mean has several different definitions depending on the context.

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## Mean free time

Molecules in a fluid constantly collide off each other.

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## Micrometre

The micrometre (International spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is an SI derived unit of length equaling (SI standard prefix "micro-".

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## Mie scattering

The Mie solution to Maxwell's equations (also known as the Lorenz–Mie solution, the Lorenz–Mie–Debye solution or Mie scattering) describes the scattering of an electromagnetic plane wave by a homogeneous sphere.

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## Millimeter of mercury

A millimeter of mercury is a manometric unit of pressure, formerly defined as the extra pressure generated by a column of mercury one millimetre high and now defined as precisely pascals.

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## Molecule

A molecule is an electrically neutral group of two or more atoms held together by chemical bonds.

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## Nanometre

The nanometre (International spelling as used by the International Bureau of Weights and Measures; SI symbol: nm) or nanometer (American spelling) is a unit of length in the metric system, equal to one billionth (short scale) of a metre (m).

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## National Institute of Standards and Technology

The National Institute of Standards and Technology (NIST) is one of the oldest physical science laboratories in the United States.

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## Nucleon

In chemistry and physics, a nucleon is either a proton or a neutron, considered in its role as a component of an atomic nucleus.

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## Optics

Optics is the branch of physics which involves the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it.

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## Ordinary differential equation

In mathematics, an ordinary differential equation (ODE) is a differential equation containing one or more functions of one independent variable and its derivatives.

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## Pair production

Pair production is the creation of an elementary particle and its antiparticle from a neutral boson.

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## Pascal (unit)

The pascal (symbol: Pa) is the SI derived unit of pressure used to quantify internal pressure, stress, Young's modulus and ultimate tensile strength.

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## Pencil (optics)

In optics, a pencil or pencil of rays is a geometric construct used to describe a beam or portion of a beam of electromagnetic radiation or charged particles, typically in the form of a narrow cone or cylinder.

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## Photon

The photon is a type of elementary particle, the quantum of the electromagnetic field including electromagnetic radiation such as light, and the force carrier for the electromagnetic force (even when static via virtual particles).

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## Physics

Physics (from knowledge of nature, from φύσις phýsis "nature") is the natural science that studies matterAt the start of The Feynman Lectures on Physics, Richard Feynman offers the atomic hypothesis as the single most prolific scientific concept: "If, in some cataclysm, all scientific knowledge were to be destroyed one sentence what statement would contain the most information in the fewest words? I believe it is that all things are made up of atoms – little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another..." and its motion and behavior through space and time and that studies the related entities of energy and force."Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular succession of events." Physics is one of the most fundamental scientific disciplines, and its main goal is to understand how the universe behaves."Physics is one of the most fundamental of the sciences. Scientists of all disciplines use the ideas of physics, including chemists who study the structure of molecules, paleontologists who try to reconstruct how dinosaurs walked, and climatologists who study how human activities affect the atmosphere and oceans. Physics is also the foundation of all engineering and technology. No engineer could design a flat-screen TV, an interplanetary spacecraft, or even a better mousetrap without first understanding the basic laws of physics. (...) You will come to see physics as a towering achievement of the human intellect in its quest to understand our world and ourselves."Physics is an experimental science. Physicists observe the phenomena of nature and try to find patterns that relate these phenomena.""Physics is the study of your world and the world and universe around you." Physics is one of the oldest academic disciplines and, through its inclusion of astronomy, perhaps the oldest. Over the last two millennia, physics, chemistry, biology, and certain branches of mathematics were a part of natural philosophy, but during the scientific revolution in the 17th century, these natural sciences emerged as unique research endeavors in their own right. Physics intersects with many interdisciplinary areas of research, such as biophysics and quantum chemistry, and the boundaries of physics are not rigidly defined. New ideas in physics often explain the fundamental mechanisms studied by other sciences and suggest new avenues of research in academic disciplines such as mathematics and philosophy. Advances in physics often enable advances in new technologies. For example, advances in the understanding of electromagnetism and nuclear physics led directly to the development of new products that have dramatically transformed modern-day society, such as television, computers, domestic appliances, and nuclear weapons; advances in thermodynamics led to the development of industrialization; and advances in mechanics inspired the development of calculus.

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## Pressure

Pressure (symbol: p or P) is the force applied perpendicular to the surface of an object per unit area over which that force is distributed.

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## Radiation length

In physics, the radiation length is a characteristic of a material, related to the energy loss of high energy, electromagnetic-interacting particles with it.

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## Radiography

Radiography is an imaging technique using X-rays to view the internal form of an object.

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## Reverberation

Reverberation, in psychoacoustics and acoustics, is a persistence of sound after the sound is produced.

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## Scattering theory

In mathematics and physics, scattering theory is a framework for studying and understanding the scattering of waves and particles.

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## Spectrum

A spectrum (plural spectra or spectrums) is a condition that is not limited to a specific set of values but can vary, without steps, across a continuum.

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## Springer Science+Business Media

Springer Science+Business Media or Springer, part of Springer Nature since 2015, is a global publishing company that publishes books, e-books and peer-reviewed journals in science, humanities, technical and medical (STM) publishing.

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## Thin film

A thin film is a layer of material ranging from fractions of a nanometer (monolayer) to several micrometers in thickness.

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## Torr

The torr (symbol: Torr) is a unit of pressure based on an absolute scale, now defined as exactly of a standard atmosphere (101.325 kPa).

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## Transmittance

Transmittance of the surface of a material is its effectiveness in transmitting radiant energy.

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## Vacuum

Vacuum is space devoid of matter.

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## Victor Weisskopf

Victor Frederick "Viki" Weisskopf (September 19, 1908 – April 22, 2002) was an Austrian-born American theoretical physicist.

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## Viscosity

The viscosity of a fluid is the measure of its resistance to gradual deformation by shear stress or tensile stress.

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## Volume fraction

In chemistry, the volume fraction φi is defined as the volume of a constituent Vi divided by the volume of all constituents of the mixture V prior to mixing: Being dimensionless, its unit is 1; it is expressed as a number, e.g., 0.18.

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## X-ray

X-rays make up X-radiation, a form of electromagnetic radiation.

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## Redirects here:

Mean Free Path, Mean FreePath, Mean path.

## References

[1] https://en.wikipedia.org/wiki/Mean_free_path