Planck's constant, denoted h, is a physical constant that is used to describe the sizes of quanta. It plays a central role in the theory of quantum mechanics, and is named after Max Planck, one of the founders of quantum theory. It has a value of approximately In science, a physical constant is a physical quantity whose numerical value does not change. ... A quantum is the smallest increment into which many physical properties are subdivided. ... Fig. ... This article is about Planck, the German physicist. ...

.

With eV·s as energy unit: An electronvolt (symbol: eV) is the amount of energy gained by a single unbound electron when it falls through an electrostatic potential difference of one volt. ... This article is about the unit of time. ...

Planck's constant has units of energy multiplied by time, which are the units of action. These units may also be written as momentum times distance (N·m·s), which are the units of angular momentum. In physics and metrology, units are standards for measurement of physical quantities that need clear definitions to be useful. ... Energy is a fundamental quantity that every physical system possesses; it allows us to predict how much work the system could be made to do, or how much heat it can exchange. ... (Clockwise from upper left) Notable Time magazine covers from May 7, 1945; July 25, 1969; December 31, 1999; September 14, 2001; and April 21, 2003. ... In physics, the action principle is an assertion about the nature of motion from which the trajectory of an object subject to forces can be determined. ... In physics, momentum is a physical quantity related to the velocity and mass of an object. ... For distance between people, see proxemics. ... This article is about the SI unit of force. ... metre or meter, see meter (disambiguation) The metre is the basic unit of length in the International System of Units. ... This article is about the unit of time. ... In physics, angular momentum intuitively measures how much the linear momentum is directed around a certain point called the origin; the moment of momentum. ...

A closely-related quantity is the reduced Planck constant (sometimes called Dirac's constant):

where π is the constant pi. This constant is pronounced as "h-bar". The minuscule, or lower-case, pi The mathematical constant π is commonly used in mathematics and physics. ...

The figures cited here are the 2002 CODATA-recommended values for the constants and their uncertainties. The 2002 CODATA results were made available in December 2003 and represent the best-known, internationally-accepted values for these constants, based on all data available through 31 December 2002. New CODATA figures are scheduled to be published approximately every four years. CODATA (Committee on Data for Science and Technology) was established in 1966 as an interdisciplinary committee of the International Council of Science (ICSU), formerly the International Council of Scientific Unions. ...

Planck's constant is used to describe quantization, a phenomenon occurring in microscopic particles such as electrons and photons in which certain physical properties occur in fixed amounts rather than assuming a continuous range of possible values. For instance, the energy E carried by a beam of light with constant frequency ν can only take on the values A particle is In particle physics, a basic unit of matter or energy. ... Properties The electron (also called negatron, commonly represented as e−) is a subatomic particle. ... In physics, the photon (from Greek φοτος, meaning light) is a quantum of excitation of the quantised electromagnetic field and is one of the elementary particles studied by quantum electrodynamics (QED) which is the oldest part of the Standard Model of particle physics. ... Energy is a fundamental quantity that every physical system possesses; it allows us to predict how much work the system could be made to do, or how much heat it can exchange. ... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye, or in a more general sense, any electromagnetic radiation in the range from infrared to ultraviolet. ... Sine waves of various frequencies; the lower waves have higher frequencies than those above. ...

It is sometimes more convenient to use the angular frequency ω=2πν, which gives Angular frequency is a measure of how fast an object is rotating In physics (specifically mechanics and electrical engineering), angular frequency ω (also called angular speed) is a scalar measure of rotation rate. ...

Many such "quantization conditions" exist. A particularly interesting condition governs the quantization of angular momentum. Let J be the total angular momentum of a system with rotational invariance, and J_z the angular momentum measured along any given direction. These quantities can only take on the values In physics, angular momentum intuitively measures how much the linear momentum is directed around a certain point called the origin; the moment of momentum. ...

Thus, may be said to be the "quantum of angular momentum".

Planck's constant also occurs in statements of Heisenberg's uncertainty principle. The uncertainty (more precisely: the standard deviation) in any position measurement, Δx, and the uncertainty in a momentum measurement along the same direction, Δp, obeys Werner Heisenberg Werner Karl Heisenberg (December 5, 1901 – February 1, 1976) was a celebrated German physicist and Nobel laureate, one of the founders of quantum mechanics. ... In quantum physics, the Heisenberg uncertainty principle, sometimes called the Heisenberg indeterminacy principle, expresses a limitation on accuracy of (nearly) simultaneous measurement of observables such as the position and the momentum of a particle. ... Uncertainty is an inevitable part of the assertion of knowledge, see Bayesian probability. ... In probability and statistics, the standard deviation is the most commonly used measure of statistical dispersion. ...

There are a number of other such pairs of physically measurable values which obey a similar rule.

On some browsers, the Unicode symbol ℎ (ℎ) is rendered as Planck's constant, and the symbol ℏ (ℏ) is rendered as Dirac's constant. In computing, Unicode is the international standard whose goal is to provide the means to encode the text of every document people want to store in computers. ...

See also

• Electromagnetic radiation
• Natural units
• Schrödinger equation
• Wave-particle duality
• Quantum Hall effect

Electromagnetic radiation or EM radiation is a combination (cross product) of oscillating electric and magnetic fields perpendicular to each other, moving through space as a wave, effectively transporting energy and momentum. ... In physics, Planck units are physical units of measurement originally proposed by Max Planck. ... In physics, the Schrödinger equation, proposed by the Austrian physicist Erwin Schrödinger in 1925, describes the time-dependence of quantum mechanical systems. ... In modern physics, duality most often refers to the paradigm underlying quantum mechanics, according to which matter or energy can exhibit properties associated with wave physics as well as classical particle mechanics. ... The quantum Hall effect is a quantum mechanical version of the Hall effect, observed in two-dimensional systems of electrons subjected to low temperatures and strong magnetic fields, in which the Hall conductance σ takes on the quantized values where e is the elementary charge and h is Plancks...

Reference

• NIST (http://physics.nist.gov/cgi-bin/cuu/Value?h) link to CODATA value