tities as electrons is described by the
*Schrödinger equation. Schrödinger
put forward this formulation of
quantum mechanics in 1926 and in
the same year showed that it was
equivalent to matrix mechanics. Taking into account the *de Broglie
wavelength, Schrödinger postulated
a wave mechanics that bears the
same relation to Newtonian mechanics as physical optics does to geometrical optics.
wave number Symbol k. The number of cycles of a wave in unit length.
It is the reciprocal of the wavelength.
wave packet A superposition of
waves with one predominant *wave
number k, but with several other
wave numbers near k. Wave packets
are useful for the analysis of scattering in *quantum mechanics. Concentrated packets of waves can be used
to describe localized particles of both
matter and *photons. The Heisenberg *uncertainty principle can be
derived from a wave-packet description of entities in quantum mechanics. The motion of a wave packet is in
accord with the motion of the corresponding classical particle, if the potential energy change across the
dimensions of the packet is very
small. This proposition is known as
Ehrenfest’s theorem, named after the
Dutch physicist Paul Ehrenfest
(1880–1933), who proved it in 1927.
wave–particle duality The concept that waves carrying energy may
have a corpuscular aspect and that
particles may have a wave aspect;
which of the two models is the more
appropriate will depend on the properties the model is seeking to explain. For example, waves of
electromagnetic radiation need to be
visualized as particles, called *photons, to explain the photoelectric effect while electrons need to be
thought of as de Broglie waves in
*electron diffraction.
wave vector A vector k associated
with a *wave number k. In the case
of free electrons the wave vector k is
related to the momentum p in
*quantum mechanics by p = បk,
where ប is the rationalized *Planck
constant. In the case of *Bloch’s theorem, the wave vector k can only have
certain values and can be thought of
as a quantum number associated
with the translational symmetry of
the crystal.
wax Any of various solid or semisolid substances. There are two main
types. Mineral waxes are mixtures of
hydrocarbons with high molecular
weights. ParafÜn wax, obtained from
*petroleum, is an example. Waxes
secreted by plants or animals are
mainly esters of fatty acids and usually have a protective function.
weak acid An *acid that is only
partially dissociated in aqueous solution.
weber Symbol Wb. The SI unit of
magnetic Ûux equal to the Ûux that,
linking a circuit of one turn, produces in it an e.m.f. of one volt as it
is reduced to zero at a uniform rate
in one second. It is named after Wilhelm Weber (1804–91).
Weissenberg technique A technique used to overcome the problem
of overlapping reÛections in the identiÜcation of the symmetry and the dimensions of a unit cell in *X-ray
crystallography. In this technique, a
screen is placed in front of the Ülm
allowing only one set of reÛections to
be exposed. The Weissenberg technique produces distorted photographs, but this can be overcome by
having a coupling between the motions of the crystal and the Ülm.
Using the precession camera tech555
Weissenberg technique
w
www.AzShimi.ir www.AzShimi.com
*Schrödinger equation. Schrödinger
put forward this formulation of
quantum mechanics in 1926 and in
the same year showed that it was
equivalent to matrix mechanics. Taking into account the *de Broglie
wavelength, Schrödinger postulated
a wave mechanics that bears the
same relation to Newtonian mechanics as physical optics does to geometrical optics.
wave number Symbol k. The number of cycles of a wave in unit length.
It is the reciprocal of the wavelength.
wave packet A superposition of
waves with one predominant *wave
number k, but with several other
wave numbers near k. Wave packets
are useful for the analysis of scattering in *quantum mechanics. Concentrated packets of waves can be used
to describe localized particles of both
matter and *photons. The Heisenberg *uncertainty principle can be
derived from a wave-packet description of entities in quantum mechanics. The motion of a wave packet is in
accord with the motion of the corresponding classical particle, if the potential energy change across the
dimensions of the packet is very
small. This proposition is known as
Ehrenfest’s theorem, named after the
Dutch physicist Paul Ehrenfest
(1880–1933), who proved it in 1927.
wave–particle duality The concept that waves carrying energy may
have a corpuscular aspect and that
particles may have a wave aspect;
which of the two models is the more
appropriate will depend on the properties the model is seeking to explain. For example, waves of
electromagnetic radiation need to be
visualized as particles, called *photons, to explain the photoelectric effect while electrons need to be
thought of as de Broglie waves in
*electron diffraction.
wave vector A vector k associated
with a *wave number k. In the case
of free electrons the wave vector k is
related to the momentum p in
*quantum mechanics by p = បk,
where ប is the rationalized *Planck
constant. In the case of *Bloch’s theorem, the wave vector k can only have
certain values and can be thought of
as a quantum number associated
with the translational symmetry of
the crystal.
wax Any of various solid or semisolid substances. There are two main
types. Mineral waxes are mixtures of
hydrocarbons with high molecular
weights. ParafÜn wax, obtained from
*petroleum, is an example. Waxes
secreted by plants or animals are
mainly esters of fatty acids and usually have a protective function.
weak acid An *acid that is only
partially dissociated in aqueous solution.
weber Symbol Wb. The SI unit of
magnetic Ûux equal to the Ûux that,
linking a circuit of one turn, produces in it an e.m.f. of one volt as it
is reduced to zero at a uniform rate
in one second. It is named after Wilhelm Weber (1804–91).
Weissenberg technique A technique used to overcome the problem
of overlapping reÛections in the identiÜcation of the symmetry and the dimensions of a unit cell in *X-ray
crystallography. In this technique, a
screen is placed in front of the Ülm
allowing only one set of reÛections to
be exposed. The Weissenberg technique produces distorted photographs, but this can be overcome by
having a coupling between the motions of the crystal and the Ülm.
Using the precession camera tech555
Weissenberg technique
w
www.AzShimi.ir www.AzShimi.com