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1. (in optics) A defect in the image formed by a lens or curved mirror. In chromatic aberration the image formed by a lens (but not a mirror) has coloured fringes as a result of the different extent to which light of different colours is refracted by glass. It is corrected by using an ...

Symbol a. The rate of increase of speed or velocity. It is measured in m s⁻². For a body moving linearly with constant acceleration ...

1. Symbol a. A thermodynamic function used in place of concentration in equilibrium constants for reactions involving nonideal gases and solutions. For example, in a reaction...

A law of the form

dB=(μoI sinθ dl)/...

A series or progression of numbers in which there is a common difference between terms, e.g. 3, 9, 15, 21,… is an arithmetic series with a common difference of 6. The general formula for the ...

The theory that, in crystals, electrons fall into allowed *energy bands, between which lie forbidden bands. Although *free-electron theory...

A device for measuring *atmospheric pressure. The mercury barometer in its simplest form consists of a glass tube about 80 cm long sealed at one end and filled with mercury. The tube is then inverted and the open end is submerged in a reservoir of mercury; the mercury column is held up by the pressure of the atmosphere acting on the surface of mercury in the reservoir. This type of device was invented by the Italian scientist Evangelista Torricelli (...

A theorem in probability theory giving the probability of an intersection of two or more sets as a product of the individual probabilities for each. It is used to calculate the probability that a particular event ...

A thermometer for measuring small changes of temperature. It consists of a mercury-in-glass thermometer with a scale covering only 5 or 6°C calibrated in hundredths of a degree. It has two mercury bulbs, the range of temperature to be measured is varied by running mercury from the upper bulb into the larger lower bulb. It is used particularly for measuring ...

A type of weak interaction (see fundamental interactions) in which an unstable atomic nucleus changes into a nucleus of the same nucleon number (...

An isotherm that takes account of the possibility that the monolayer in the *Langmuir adsorption isotherm can act as a substrate for further adsorption. The BET isotherm (named after ...

Newton’s work gave a mathematical basis for the universe on a large scale. However, the data available at the time suggested a static unchanging universe. This could not easily be explained in the context of the law of gravitation, since all bodies in the universe attract all other bodies with the force of gravity. Newton realized that there was only one solution to this problem: in a static universe, matter had to be uniformly spread throughout an infinitely large space. In ...

The distribution of the number of successes in an experiment in which there are two possible outcomes, success and failure. The probability of ...

A rule for the expansion of a binomial expression (expression consisting of the sum of two variables raised to a given power). The general binomial expression (...

A geometrical representation of a two-state system in *quantum mechanics in which the system is represented by a sphere. An example of a quantum-mechanical system that can be represented in this way is the ...

Symbol k or k _B. The ratio of the universal gas constant (R) to the Avogadro constant (...

An equation used in the study of a collection of particles in *nonequilibrium statistical mechanics, particularly their transport properties. The Boltzmann equation describes a quantity called the ...

A cycle of reactions used for calculating the lattice energies of ionic crystalline solids. For a compound MX, the lattice energy is the enthalpy of the reaction...

When a beam of X-rays (wavelength λ) strikes a crystal surface in which the layers of atoms or ions are separated by a distance ...

A series of mathematical techniques developed independently by Isaac *Newton and Gottfried Leibniz (1646–1716). Differential calculus treats a continuously varying quantity as if it consisted of an infinitely large number of infinitely small changes. For example, the velocity ...