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Perpendicular

Denoting the latest stage of English Gothic church architecture, prevalent from the late 14th to mid 16th centuries and characterized by broad arches, elaborate fan vaulting, and large ...

isometric

isometric   Quick reference

A Dictionary of Chemistry (7 ed.)

Reference type:
Subject Reference
Current Version:
2016
Subject:
Science and technology, Chemistry
Length:
40 words

...1. (in crystallography) Denoting a system in which the axes are perpendicular to each other, as in cubic crystals. 2. Denoting a line on a graph illustrating the way in which temperature and pressure are interrelated at constant...

anisotropic

anisotropic   Quick reference

A Dictionary of Chemistry (7 ed.)

Reference type:
Subject Reference
Current Version:
2016
Subject:
Science and technology, Chemistry
Length:
56 words

... Denoting a medium in which certain physical properties are different in different directions. Wood, for instance, is an anisotropic material: its strength along the grain differs from that perpendicular to the grain. Single crystals that are not cubic are anisotropic with respect to some physical properties, such as the transmission of electromagnetic radiation. Compare isotropic...

tie line

tie line   Quick reference

A Dictionary of Chemistry (7 ed.)

Reference type:
Subject Reference
Current Version:
2016
Subject:
Science and technology, Chemistry
Length:
50 words

...line A horizontal line in a liquid–vapour phase diagram that is perpendicular to an isopleth . The starting point is the first point at which the liquid can coexist with its vapour as the pressure is reduced; the end point is the point beyond which only vapour is...

dihedral

dihedral   Quick reference

A Dictionary of Chemistry (7 ed.)

Reference type:
Subject Reference
Current Version:
2016
Subject:
Science and technology, Chemistry
Length:
52 words

... ( dihedron ) An angle formed by the intersection of two planes (e.g. two faces of a polyhedron). The dihedral angle is the angle formed by taking a point on the line of intersection and drawing two lines from this point, one in each plane, perpendicular to the line of...

allenes

allenes   Quick reference

A Dictionary of Chemistry (7 ed.)

Reference type:
Subject Reference
Current Version:
2016
Subject:
Science and technology, Chemistry
Length:
125 words

...example is 1,2-propadiene, CH 2 CCH 2 . Allenes are dienes with typical reactions of alkenes. Under basic conditions, they often convert to alkynes. In an allene, the two double bonds lie in planes that are perpendicular to each other. Consequently, in an allene of the type R 1 R 2 C=C=CR 3 R 4 , the groups R 1 and R 2 lie in a plane perpendicular to the plane containing R 3 and R 4 . Under these circumstances, the molecule is chiral and can show optical...

Brillouin zone

Brillouin zone   Quick reference

A Dictionary of Chemistry (7 ed.)

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Subject Reference
Current Version:
2016
Subject:
Science and technology, Chemistry
Length:
75 words

...zone A cell in a reciprocal lattice. The first Brillouin zone is the cell of smallest volume enclosed by those planes that are perpendicular bisectors of reciprocal lattice vectors. Higher Brillouin zones also exist. Brillouin zones are used in the theory of energy levels in a periodic potential, as in a crystal. They are named after the French physicist Léon Brillouin ( 1889–1969 ), who introduced them into the theory of crystals in 1930...

Wigner–Seitz cell

Wigner–Seitz cell   Quick reference

A Dictionary of Chemistry (7 ed.)

Reference type:
Subject Reference
Current Version:
2016
Subject:
Science and technology, Chemistry
Length:
65 words

...cell A polyhedron in a crystal that is bounded by planes formed by perpendicular bisectors of bonds between lattice sites. The Wigner–Seitz cell was used by Hungarian-born US physicist Eugene Wigner ( 1902–95 ) and Frederick Seitz ( 1911–2008 ) in 1933 in the course of their analysis of the cohesion of metals. The concept has been used extensively in the theory of...

liquid crystal

liquid crystal   Quick reference

A Dictionary of Chemistry (7 ed.)

Reference type:
Subject Reference
Current Version:
2016
Subject:
Science and technology, Chemistry
Length:
70 words

...direction, but otherwise randomly arranged. Cholesteric and smectic liquid crystals also have aligned molecules, which are arranged in distinct layers. In cholesteric crystals, the axes of the molecules are parallel to the plane of the layers; in smectic crystals they are perpendicular...

apical

apical   Quick reference

A Dictionary of Chemistry (7 ed.)

Reference type:
Subject Reference
Current Version:
2016
Subject:
Science and technology, Chemistry
Length:
80 words

...For example, in a trigonal bipyramid the two bonds aligned through the central atom are the apical bonds and the groups attached to these bonds are in apical positions. The three other bonds and positions are equatorial . Similarly, in a square pyramidal structure the bond perpendicular to the base of the pyramid is the apical bond. The four other coplanar bonds (and positions) are said to be basal...

polarizer

polarizer   Quick reference

A Dictionary of Chemistry (7 ed.)

Reference type:
Subject Reference
Current Version:
2016
Subject:
Science and technology, Chemistry
Length:
122 words

...is unable to detect that light is polarized, it is necessary to use an analyser to detect the direction of polarization. Crossing a polarizer and analyser causes extinction of the light, i.e. if the plane of polarization of the polarizer and the plane of the analyser are perpendicular, no light is transmitted when the polarizer and analyser are combined. Both a polarizer and an analyser are components of a polarimeter...

Schoenflies system

Schoenflies system   Quick reference

A Dictionary of Chemistry (7 ed.)

Reference type:
Subject Reference
Current Version:
2016
Subject:
Science and technology, Chemistry
Length:
282 words

...of the n -fold axis). C nh groups, in addition to the n -fold rotation axis, have a mirror plane perpendicular to the axis. S n groups have an n -fold rotation-reflection axis. D n groups have an n -fold rotation axis and a two-fold axis perpendicular to the n -fold axis (and two-fold axes associated with the existence of the n -fold axis). D nh groups have all the symmetry operations of D n and also a mirror plane perpendicular to the n -fold axis. D nd groups contain all the symmetry operations of D n and also mirror planes that...

Pockels cell

Pockels cell   Quick reference

A Dictionary of Chemistry (7 ed.)

Reference type:
Subject Reference
Current Version:
2016
Subject:
Science and technology, Chemistry
Length:
153 words

...light when a potential difference is applied. A Pockels cell can be made part of a laser cavity. When this happens, a change of polarization occurs when light is reflected from a mirror and the light that is polarized in one plane is converted into light polarized in the perpendicular plane. The effect is that the reflected light does not stimulate emission. When the Pockels cell is turned off the polarization does not occur and the energy in the cavity can be released in the form of a pulse of stimulated radiation. The Pockels cell is named after Friedrich...

polarization of light

polarization of light   Quick reference

A Dictionary of Chemistry (7 ed.)

Reference type:
Subject Reference
Current Version:
2016
Subject:
Science and technology, Chemistry
Length:
165 words

...of light The process of confining the vibrations of the electric vector of light waves to one direction. In unpolarized light the electric field vibrates in all directions perpendicular to the direction of propagation. After reflection or transmission through certain substances ( see Polaroid ) the electric field is confined to one direction and the radiation is said to be plane-polarized light . The plane of plane-polarized light can be rotated when it passes through certain substances ( see optical activity ). In circularly polarized light ,...

surface tension

surface tension   Quick reference

A Dictionary of Chemistry (7 ed.)

Reference type:
Subject Reference
Current Version:
2016
Subject:
Science and technology, Chemistry
Length:
174 words

...interior of a liquid experiences interactions from other molecules equally from all sides, whereas a molecule at the surface is only affected by molecules below it in the liquid. The surface tension is defined as the force acting over the surface per unit length of surface perpendicular to the force. It is measured in newtons per metre. It can equally be defined as the energy required to increase the surface area isothermally by one square metre, i.e. it can be measured in joules per metre squared (which is equivalent to N m −1 ). The property of surface...

Zeeman effect

Zeeman effect   Quick reference

A Dictionary of Chemistry (7 ed.)

Reference type:
Subject Reference
Current Version:
2016
Subject:
Science and technology, Chemistry
Length:
167 words

...effect The splitting of the lines in a spectrum when the source of the spectrum is exposed to a magnetic field. It was discovered in 1896 by Pieter Zeeman ( 1865–1943 ). In the normal Zeeman effect a single line is split into three if the field is perpendicular to the light path or two lines if the field is parallel to the light path. This effect can be explained by classical electrodynamics in terms of the speeding up and slowing down of orbital electrons in the source as a result of the applied field. It has also been explained in terms of the ...

moment of inertia

moment of inertia   Quick reference

A Dictionary of Chemistry (7 ed.)

Reference type:
Subject Reference
Current Version:
2016
Subject:
Science and technology, Chemistry
Length:
311 words

...with a body that is rotating about an axis. If a body consists of i particles of mass m i a perpendicular distance r i from an axis of rotation, the moment of inertia I of the body about that axis of rotation is given by I  = ∑ m i r i 2 . The moment of inertia of a body is an important quantity because it is the analogue for rotational motion of mass for linear motion. In a molecule all rotational motion can be analysed using three perpendicular axes of rotation. Each of these has a moment of inertia associated with it. To a first approximation,...

Lamb-dip spectroscopy

Lamb-dip spectroscopy   Quick reference

A Dictionary of Chemistry (7 ed.)

Reference type:
Subject Reference
Current Version:
2016
Subject:
Science and technology, Chemistry
Length:
194 words

...can absorb radiation. The beam is then reflected back through the sample so that radiation is absorbed by molecules moving at exactly this same speed, except that they are moving away from the mirror. If the radiation is exactly at the absorption peak, only molecules moving perpendicular to the line of the beam (which hence have no Doppler shift) absorb both in the initial path and the reflected path of the radiation. Since molecules being excited in the initial path leave fewer molecules to be excited in the return path this causes a less intense absorption...

magnetic moment

magnetic moment   Quick reference

A Dictionary of Chemistry (7 ed.)

Reference type:
Subject Reference
Current Version:
2016
Subject:
Science and technology, Chemistry
Length:
250 words

...area moment ) is the ratio T max / B . In the Kennelly approach the quantity (also called magnetic dipole moment ) is T max / H . In the case of a magnet placed in a magnetic field of field strength H , the maximum torque T max occurs when the axis of the magnet is perpendicular to the field. In the case of a coil of N turns and area A carrying a current I , the magnetic moment can be shown to be m  =  T / B  =  NIA or m  =  T / H  =  μ ‎ NIA . Magnetic moments are measured in A m 2 . An orbital electron has an orbital magnetic moment IA ,...

Kerr effect

Kerr effect   Quick reference

A Dictionary of Chemistry (7 ed.)

Reference type:
Subject Reference
Current Version:
2016
Subject:
Science and technology, Chemistry
Length:
337 words
Illustration(s):
2

...is characteristic of the substance and approximately inversely proportional to the thermodynamic temperature. The Kerr shutter consists of a Kerr cell filled with a liquid, such as nitrobenzene, placed between two crossed polarizers; the electric field is arranged to be perpendicular to the axis of the light beam and at 45° to the axis of the polarizers. In the absence of a field there is no optical path through the device. When the field is switched on the nitrobenzene becomes doubly refracting and a path opens between the crossed...

allenes

allenes  

Compounds that contain the group >C=C=C<, in which three carbon atoms are linked by two adjacent double bonds. The outer carbon atoms are each linked to two other atoms or groups by single bonds. The ...

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