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restitution coefficient

Overview page. Subjects: Physics.

Symbol e. A measure of the elasticity of colliding bodies. For two spheres moving in the same straight line, e = (v 2v 1)/(u 1u 2),...

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reverberation time

Overview page. Subjects: Physics.

The time taken for the energy density of a sound to fall to the threshold of audibility from a value 106 times as great; i.e. a fall of 60 decibels. It is an important characteristic of an...

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relational theory

Overview page. Subjects: Physics.

A type of theory in which absolute space and absolute time do not occur, with the theory depending on relationships between events. Newtonian mechanics is not a relational theory but the...

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resistance thermometer

Overview page. Subjects: Physics.

A thermometer in which the sensing element consists of a substance whose electrical resistance varies with temperature. Such sensors are both sensitive and rugged, and are commonly employed...

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resistivity

Overview page. Subjects: Physics.

Symbol ρ. A measure of a material's ability to oppose the flow of an electric current. The resistivity of a material is given by RA/l, where R is the resistance of a uniform specimen of the...

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resonant cavity

Overview page. Subjects: Physics.

A closed space within a conductor in which an electromagnetic field can be made to oscillate at frequencies above those at which a resonant circuit will operate. The resonant frequency of...

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resonating valence bond theory

Overview page. Subjects: Physics.

An extension of valence bond theory to solids in which there is quantum-mechanical resonance between different structures throughout the solid. Attempts have been made to describe...

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ring main

Overview page. Subjects: Physics.

1. A domestic wiring system in which all the power outlets have their own individual fuses and in which the outlets are connected in parallel to a ring circuit, which starts...

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Riemannian geometry

Overview page. Subjects: Physics.

A type of non-Euclidean geometry proposed by the German mathematician George Friedrich Bernhard Riemann (1826–66) in 1854. It is ideally suited to describing the curvature of space–time in...

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