Matura diamond See zircon.
Maxwell, James Clerk (1831–79)
British physicist, born in Edinburgh,
who held academic posts at Aberdeen, London, and Cambridge. In
the 1860s he was one of the founders
of the *kinetic theory of gases, but
his best-known work was a mathematical analysis of electromagnetic
radiation, published in 1864.
Maxwell–Boltzmann distribution A law describing the distribution of speeds among the molecules
of a gas. In a system consisting of N
molecules that are independent of
each other except that they exchange
energy on collision, it is clearly impossible to say what velocity any particular molecule will have. However,
statistical statements regarding certain functions of the molecules were
worked out by James Clerk *Maxwell and Ludwig *Boltzmann. One
form of their law states that
n = Nexp(–E/RT), where n is the number of molecules with energy in excess of E, T is the thermodynamic
temperature, and R is the *gas constant.
Maxwell’s demon An imaginary
creature that is able to open and shut
a partition dividing two volumes of a
gas in a container, when the two volumes are initially at the same temperature. The partition operated by
the demon is only opened to allow
fast molecules through. Such a
process would make the volume of
gas containing the fast molecules
hotter than it was at the start; the
volume of gas remaining would accordingly become cooler. This
process would be a violation of the
second law of *thermodynamics and
therefore cannot occur. Maxwell’s
demon was invented by James Clerk
Maxwell in a letter written in 1867 to
show that the second law of thermodynamics has its origins in *statistical mechanics, although the name
was suggested by the Scottish scientist Sir William Thomson
(1824–1907; subsequently Lord
Kelvin).
Maxwell’s thermodynamic
equations Equations in thermodynamics for a given mass of a homogeneous system, relating the entropy
(S), pressure (p), volume (V), and thermodynamic temperature (T). The
four equations are:
(∂T/∂V) s = –(∂p/∂S) V ;
∂T/∂p) s = –(∂V/∂S) p ;
(∂V/∂T) p = –(∂S/∂p) T ;
(∂S/∂V) T = –(∂p/∂T) V .
Mayer f-function A quantity that
occurs in the calculation of virial
coefÜcients; it is deÜned by f =
exp(–V 2 /kT) – 1, where V 2 is the twobody interaction potential energy, k
is the *Boltzmann constant, and T is
the thermodynamic temperature. It
is related to the second virial coefÜcient B by:
B = (–N A /V)∫ fdr 1 dr 2 ,
where N A is the Avogadro number
and V is the volume of the system.
This equation simpliÜed to:
B = –2πN A ∫
∞
0 fr
2
dr
in the case of closed-shell atoms and
octahedral and tetrahedral molecules. When particles are so far
apart that the interaction V → 0,
then f → 0 also, but when the particles are so close together that the interaction V → ∞, then f → –1. This
enables strong repulsive interactions
between particles to be analysed in
terms of f but not of V. The function
is named after the US physicist
Joseph Mayer.
Mayer’s test A general *presumptive test for cocaine, morphine,
heroin, and other alkaloids. Mayer’s
reagent is a solution of potassium
mercury iodide in water. A positive
345
Mayer’s test
m
www.AzShimi.ir www.AzShimi.com
Maxwell, James Clerk (1831–79)
British physicist, born in Edinburgh,
who held academic posts at Aberdeen, London, and Cambridge. In
the 1860s he was one of the founders
of the *kinetic theory of gases, but
his best-known work was a mathematical analysis of electromagnetic
radiation, published in 1864.
Maxwell–Boltzmann distribution A law describing the distribution of speeds among the molecules
of a gas. In a system consisting of N
molecules that are independent of
each other except that they exchange
energy on collision, it is clearly impossible to say what velocity any particular molecule will have. However,
statistical statements regarding certain functions of the molecules were
worked out by James Clerk *Maxwell and Ludwig *Boltzmann. One
form of their law states that
n = Nexp(–E/RT), where n is the number of molecules with energy in excess of E, T is the thermodynamic
temperature, and R is the *gas constant.
Maxwell’s demon An imaginary
creature that is able to open and shut
a partition dividing two volumes of a
gas in a container, when the two volumes are initially at the same temperature. The partition operated by
the demon is only opened to allow
fast molecules through. Such a
process would make the volume of
gas containing the fast molecules
hotter than it was at the start; the
volume of gas remaining would accordingly become cooler. This
process would be a violation of the
second law of *thermodynamics and
therefore cannot occur. Maxwell’s
demon was invented by James Clerk
Maxwell in a letter written in 1867 to
show that the second law of thermodynamics has its origins in *statistical mechanics, although the name
was suggested by the Scottish scientist Sir William Thomson
(1824–1907; subsequently Lord
Kelvin).
Maxwell’s thermodynamic
equations Equations in thermodynamics for a given mass of a homogeneous system, relating the entropy
(S), pressure (p), volume (V), and thermodynamic temperature (T). The
four equations are:
(∂T/∂V) s = –(∂p/∂S) V ;
∂T/∂p) s = –(∂V/∂S) p ;
(∂V/∂T) p = –(∂S/∂p) T ;
(∂S/∂V) T = –(∂p/∂T) V .
Mayer f-function A quantity that
occurs in the calculation of virial
coefÜcients; it is deÜned by f =
exp(–V 2 /kT) – 1, where V 2 is the twobody interaction potential energy, k
is the *Boltzmann constant, and T is
the thermodynamic temperature. It
is related to the second virial coefÜcient B by:
B = (–N A /V)∫ fdr 1 dr 2 ,
where N A is the Avogadro number
and V is the volume of the system.
This equation simpliÜed to:
B = –2πN A ∫
∞
0 fr
2
dr
in the case of closed-shell atoms and
octahedral and tetrahedral molecules. When particles are so far
apart that the interaction V → 0,
then f → 0 also, but when the particles are so close together that the interaction V → ∞, then f → –1. This
enables strong repulsive interactions
between particles to be analysed in
terms of f but not of V. The function
is named after the US physicist
Joseph Mayer.
Mayer’s test A general *presumptive test for cocaine, morphine,
heroin, and other alkaloids. Mayer’s
reagent is a solution of potassium
mercury iodide in water. A positive
345
Mayer’s test
m
www.AzShimi.ir www.AzShimi.com