# Temperature

temperaturesair temperaturewarmhotsubzerosurface temperatureTabsolute temperaturehigh temperaturemean temperature
Temperature is a physical quantity that expresses the subjective sensations of hot and cold.wikipedia
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### Thermodynamic equilibrium

equilibriumequilibrium statelocal thermodynamic equilibrium
When a body has no macroscopic chemical reactions or flows of matter or energy, it is said to be in its own internal state of thermodynamic equilibrium.
A thermodynamic system in a state of internal thermodynamic equilibrium has a spatially uniform temperature.

A definite sense of greater hotness can be had, independently of calorimetry, of thermodynamics, and of properties of particular materials, from Wien's displacement law of thermal radiation: the temperature of a bath of thermal radiation is proportional, by a universal constant, to the frequency of the maximum of its frequency spectrum; this frequency is always positive, but can have values that tend to zero.
All matter with a temperature greater than absolute zero emits thermal radiation.

### Thermodynamics

thermodynamicthermodynamicallyclassical thermodynamics
A definite sense of greater hotness can be had, independently of calorimetry, of thermodynamics, and of properties of particular materials, from Wien's displacement law of thermal radiation: the temperature of a bath of thermal radiation is proportional, by a universal constant, to the frequency of the maximum of its frequency spectrum; this frequency is always positive, but can have values that tend to zero. Besides the internationally agreed Kelvin scale, there is also a thermodynamic temperature scale, invented by Kelvin, also with its numerical zero at the absolute zero of temperature, but directly relating to purely macroscopic thermodynamic concepts, including the macroscopic entropy, though microscopically referable to the Gibbs statistical mechanical definition of entropy for the canonical ensemble, that takes interparticle potential energy into account, as well as independent particle motion, so that it can account for measurements of temperatures near absolute zero.
Thermodynamics is the branch of physics that deals with heat and temperature, and their relation to energy, work, radiation, and properties of matter.

### Thermodynamic temperature

absolute temperaturetemperatureabsolute
Besides the internationally agreed Kelvin scale, there is also a thermodynamic temperature scale, invented by Kelvin, also with its numerical zero at the absolute zero of temperature, but directly relating to purely macroscopic thermodynamic concepts, including the macroscopic entropy, though microscopically referable to the Gibbs statistical mechanical definition of entropy for the canonical ensemble, that takes interparticle potential energy into account, as well as independent particle motion, so that it can account for measurements of temperatures near absolute zero.
Thermodynamic temperature is the absolute measure of temperature and is one of the principal parameters of thermodynamics.

### Triple point

triple point of waterhigh pressureTriple Point cell
This scale has a reference temperature at the triple point of water, the numerical value of which is defined by measurements using the aforementioned internationally agreed Kelvin scale.
In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium.

### Zero-point energy

zero point energyzero-point fieldzero-point
Microscopically, in the description of quantum mechanics, however, matter still has zero-point energy even at absolute zero, because of the uncertainty principle.
Temperature, for example, arises from the intensity of random particle motion caused by kinetic energy (known as brownian motion).

### Planck's law

Measurement of the spectrum of electromagnetic radiation from an ideal three-dimensional black body can provide an accurate temperature measurement because the frequency of maximum spectral radiance of black-body radiation is directly proportional to the temperature of the black body; this is known as Wien's displacement law and has a theoretical explanation in Planck's law and the Bose–Einstein law.
Planck's law describes the spectral density of electromagnetic radiation emitted by a black body in thermal equilibrium at a given temperature T, when there is no net flow of matter or energy between the body and its environment.

### Chemistry

chemistchemicalApplied Chemistry
Temperature is important in all fields of natural science, including physics, chemistry, Earth science, medicine, and biology, as well as most aspects of daily life.
A phase is a set of states of a chemical system that have similar bulk structural properties, over a range of conditions, such as pressure or temperature.

### International System of Units

SISI unitsSI unit
The most common scales are the Celsius scale (formerly called centigrade), denoted °C, the Fahrenheit scale (denoted °F), and the Kelvin scale (denoted K), the latter of which is predominantly used for scientific purposes by conventions of the International System of Units (SI).

### Equipartition theorem

equipartitionequipartition of energyall modes excited more or less equally
The equipartition theorem of kinetic theory asserts that each classical degree of freedom of a freely moving particle has an average kinetic energy of
In classical statistical mechanics, the equipartition theorem relates the temperature of a system to its average energies.

### Black body

blackbodyblack-bodyblack bodies
Measurement of the spectrum of electromagnetic radiation from an ideal three-dimensional black body can provide an accurate temperature measurement because the frequency of maximum spectral radiance of black-body radiation is directly proportional to the temperature of the black body; this is known as Wien's displacement law and has a theoretical explanation in Planck's law and the Bose–Einstein law.
The radiation is emitted according to Planck's law, meaning that it has a spectrum that is determined by the temperature alone (see figure at right), not by the body's shape or composition.

### Boltzmann constant

Boltzmann's constantkthermal voltage
Referring to the Boltzmann constant, to the Maxwell–Boltzmann distribution, and to the Boltzmann statistical mechanical definition of entropy, as distinct from the Gibbs definition, for independently moving microscopic particles, disregarding interparticle potential energy, by international agreement, a temperature scale is defined and said to be absolute because it is independent of the characteristics of particular thermometric substances and thermometer mechanisms.
or k), named after its discoverer, Ludwig Boltzmann, is a physical constant that relates the average relative kinetic energy of particles in a gas with the temperature of the gas.

### Density

densemass densitydensities
In general, density can be changed by changing either the pressure or the temperature.

### Measurement

measuremeasuringmeasurements
Temperature is measured with a thermometer.

### Kinetic theory of gases

kinetic theorythermal motionkinetic
Kinetic theory provides a microscopic account of temperature for some bodies of material, especially gases, based on macroscopic systems' being composed of many microscopic particles, such as molecules and ions of various species, the particles of a species being all alike.
Kinetic molecular theory defines temperature in its own way, in contrast with the thermodynamic definition.

### Heat capacity

heat capacitiesthermal capacityspecific heat
Thus a diatomic gas will require more energy input to increase its temperature by a certain amount, i.e. it will have a greater heat capacity than a monatomic gas.
Heat capacity or thermal capacity is a physical property of matter, defined as the amount of heat to be supplied to a given mass of a material to produce a unit change in its temperature.

### Physical quantity

physical quantitiesquantitiesquantity
Temperature is a physical quantity that expresses the subjective sensations of hot and cold.

### Ideal gas

idealideal gasesideal-gas
In an ideal gas, and in other theoretically understood bodies, the Kelvin temperature is defined to be proportional to the average kinetic energy of non-interactively moving microscopic particles, which can be measured by suitable techniques.
Generally, a gas behaves more like an ideal gas at higher temperature and lower pressure, as the potential energy due to intermolecular forces becomes less significant compared with the particles' kinetic energy, and the size of the molecules becomes less significant compared to the empty space between them.

### Kelvin

KkelvinsKelvin scale
The most common scales are the Celsius scale (formerly called centigrade), denoted °C, the Fahrenheit scale (denoted °F), and the Kelvin scale (denoted K), the latter of which is predominantly used for scientific purposes by conventions of the International System of Units (SI).
The kelvin is the base unit of temperature in the International System of Units (SI), having the unit symbol K. It is named after the Belfast-born, Glasgow University engineer and physicist William Thomson, 1st Baron Kelvin (1824–1907).

### Fahrenheit

°FFdegrees Fahrenheit
The most common scales are the Celsius scale (formerly called centigrade), denoted °C, the Fahrenheit scale (denoted °F), and the Kelvin scale (denoted K), the latter of which is predominantly used for scientific purposes by conventions of the International System of Units (SI).
The lower defining point, 0 ℉, was established as the freezing temperature of a solution of brine made from equal parts of ice, water and a salt (ammonium chloride).

### Calorimetry

calorimetriccalorimeterconstant pressure calorimetry
A definite sense of greater hotness can be had, independently of calorimetry, of thermodynamics, and of properties of particular materials, from Wien's displacement law of thermal radiation: the temperature of a bath of thermal radiation is proportional, by a universal constant, to the frequency of the maximum of its frequency spectrum; this frequency is always positive, but can have values that tend to zero. Especially, it was used for calorimetry, which contributed greatly to the discovery of thermodynamics.
Scottish physician and scientist Joseph Black, who was the first to recognize the distinction between heat and temperature, is said to be the founder of the science of calorimetry.

### Entropy

entropicentropicallyspecific entropy
Besides the internationally agreed Kelvin scale, there is also a thermodynamic temperature scale, invented by Kelvin, also with its numerical zero at the absolute zero of temperature, but directly relating to purely macroscopic thermodynamic concepts, including the macroscopic entropy, though microscopically referable to the Gibbs statistical mechanical definition of entropy for the canonical ensemble, that takes interparticle potential energy into account, as well as independent particle motion, so that it can account for measurements of temperatures near absolute zero. Referring to the Boltzmann constant, to the Maxwell–Boltzmann distribution, and to the Boltzmann statistical mechanical definition of entropy, as distinct from the Gibbs definition, for independently moving microscopic particles, disregarding interparticle potential energy, by international agreement, a temperature scale is defined and said to be absolute because it is independent of the characteristics of particular thermometric substances and thermometer mechanisms.
Boltzmann's constant, and therefore entropy, have dimensions of energy divided by temperature, which has a unit of joules per kelvin (J⋅K −1 ) in the International System of Units (or kg⋅m 2 ⋅s −2 ⋅K −1 in terms of base units).

### Scale of temperature

temperature scaleempirical temperature scaleempirical temperature scales
Experimental physicists, for example Galileo and Newton, found that there are indefinitely many empirical temperature scales.
Scale of temperature is a way to measure temperature quantitatively.

### Newton's law of cooling

an empirical law of coolingcooling curveempirical law of cooling
Experimental physicists, for example Galileo and Newton, found that there are indefinitely many empirical temperature scales.
Newton's law of cooling states that the rate of heat loss of a body is directly proportional to the difference in the temperatures between the body and its surroundings. The law is frequently qualified to include the condition that the temperature difference is small and the nature of heat transfer mechanism remains the same.

### Johnson–Nyquist noise

thermal noiseJohnson noisenoise
In a given frequency band, the noise-power has equal contributions from every frequency and is called Johnson noise.
where is the noise power density in (W/Hz), k_B is the Boltzmann constant and T is the temperature.