phere, especially by factory chimneys.
farad Symbol F. The SI unit of capacitance, being the capacitance of a
capacitor that, if charged with one
coulomb, has a potential difference
of one volt between its plates. 1 F = 1
C V
–1
. The farad itself is too large for
most applications; the practical unit
is the microfarad (10
–6 F). The unit is
named after Michael *Faraday.
Faraday, Michael (1791–1867)
British chemist and physicist, who received little formal education. He
started to experiment on electricity
and in 1812 attended lectures by Sir
Humphry *Davy at the Royal Institution; a year later he became Davy’s
assistant. He remained at the Institution until 1861. Faraday’s chemical
discoveries include the liquefaction
of chlorine (1823) and benzene (1825)
as well as the laws of electrolysis (see
faraday’s laws). He is also remembered for his work in physics: in
1821 he demonstrated electromagnetic rotation (the principle of the
electric motor) and in 1832 discovered electromagnetic induction (the
principle of the dynamo).
Faraday constant Symbol F. The
electric charge carried by one mole
of electrons or singly ionized ions,
i.e. the product of the *Avogadro
constant and the charge on an electron (disregarding sign). It has the
value 9.648 5309(29) × 10
4 coulombs
per mole. This number of coulombs
is sometimes treated as a unit of electric charge called the faraday.
Faraday’s laws Two laws describing electrolysis:
(1) The amount of chemical change
during electrolysis is proportional to
the charge passed.
(2) The charge required to deposit or
liberate a mass m is given by Q =
Fmz/M, where F is the Faraday constant, z the charge of the ion, and M
the relative ionic mass.
These are the modern forms of the
laws. Originally, they were stated by
Michael *Faraday in a different form:
(1) The amount of chemical change
produced is proportional to the quantity of electricity passed.
(2) The amount of chemical change
produced in different substances by a
Üxed quantity of electricity is proportional to the electrochemical equivalent of the substance.
fast-atom bombardment mass
spectroscopy (FAB mass spectroscopy) A technique in *mass spectroscopy in which ions are produced
by bombardment with high-energy
neutral atoms or molecules. It is used
for samples that are nonvolatile or
are thermally unstable.
fat A mixture of lipids, chieÛy
*triglycerides, that is solid at normal
body temperatures. Fats occur widely
in plants and animals as a means of
storing food energy, having twice the
caloriÜc value of carbohydrates. In
mammals, fat is deposited in a layer
beneath the skin (subcutaneous fat)
and deep within the body as a specialized adipose tissue.
Fats derived from plants and Üsh
generally have a greater proportion
of unsaturated *fatty acids than
those from mammals. Their melting
points thus tend to be lower, causing
a softer consistency at room temperatures. Highly unsaturated fats are liquid at room temperatures and are
therefore more properly called *oils.
fatty acid An organic compound
consisting of a hydrocarbon chain
and a terminal carboxyl group (see
carboxylic acids). Chain length
ranges from one hydrogen atom
(methanoic, or formic, acid, HCOOH)
to nearly 30 carbon atoms. Ethanoic
(acetic), propanoic (propionic), and
butanoic (butyric) acids are imporfarad
220
f
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farad Symbol F. The SI unit of capacitance, being the capacitance of a
capacitor that, if charged with one
coulomb, has a potential difference
of one volt between its plates. 1 F = 1
C V
–1
. The farad itself is too large for
most applications; the practical unit
is the microfarad (10
–6 F). The unit is
named after Michael *Faraday.
Faraday, Michael (1791–1867)
British chemist and physicist, who received little formal education. He
started to experiment on electricity
and in 1812 attended lectures by Sir
Humphry *Davy at the Royal Institution; a year later he became Davy’s
assistant. He remained at the Institution until 1861. Faraday’s chemical
discoveries include the liquefaction
of chlorine (1823) and benzene (1825)
as well as the laws of electrolysis (see
faraday’s laws). He is also remembered for his work in physics: in
1821 he demonstrated electromagnetic rotation (the principle of the
electric motor) and in 1832 discovered electromagnetic induction (the
principle of the dynamo).
Faraday constant Symbol F. The
electric charge carried by one mole
of electrons or singly ionized ions,
i.e. the product of the *Avogadro
constant and the charge on an electron (disregarding sign). It has the
value 9.648 5309(29) × 10
4 coulombs
per mole. This number of coulombs
is sometimes treated as a unit of electric charge called the faraday.
Faraday’s laws Two laws describing electrolysis:
(1) The amount of chemical change
during electrolysis is proportional to
the charge passed.
(2) The charge required to deposit or
liberate a mass m is given by Q =
Fmz/M, where F is the Faraday constant, z the charge of the ion, and M
the relative ionic mass.
These are the modern forms of the
laws. Originally, they were stated by
Michael *Faraday in a different form:
(1) The amount of chemical change
produced is proportional to the quantity of electricity passed.
(2) The amount of chemical change
produced in different substances by a
Üxed quantity of electricity is proportional to the electrochemical equivalent of the substance.
fast-atom bombardment mass
spectroscopy (FAB mass spectroscopy) A technique in *mass spectroscopy in which ions are produced
by bombardment with high-energy
neutral atoms or molecules. It is used
for samples that are nonvolatile or
are thermally unstable.
fat A mixture of lipids, chieÛy
*triglycerides, that is solid at normal
body temperatures. Fats occur widely
in plants and animals as a means of
storing food energy, having twice the
caloriÜc value of carbohydrates. In
mammals, fat is deposited in a layer
beneath the skin (subcutaneous fat)
and deep within the body as a specialized adipose tissue.
Fats derived from plants and Üsh
generally have a greater proportion
of unsaturated *fatty acids than
those from mammals. Their melting
points thus tend to be lower, causing
a softer consistency at room temperatures. Highly unsaturated fats are liquid at room temperatures and are
therefore more properly called *oils.
fatty acid An organic compound
consisting of a hydrocarbon chain
and a terminal carboxyl group (see
carboxylic acids). Chain length
ranges from one hydrogen atom
(methanoic, or formic, acid, HCOOH)
to nearly 30 carbon atoms. Ethanoic
(acetic), propanoic (propionic), and
butanoic (butyric) acids are imporfarad
220
f
www.AzShimi.ir www.AzShimi.com