electrolytic separation A method
of separating isotopes by exploiting
the different rates at which they are
released in electrolysis. It was formerly used for separating deuterium
and hydrogen. On electrolysis of
water, hydrogen is formed at the
cathode more readily than deuterium, thus the water becomes enriched with deuterium oxide.
electromagnetic radiation Energy resulting from the acceleration
of electric charge and the associated
electric Üelds and magnetic Üelds.
The energy can be regarded as waves
propagated through space (requiring
no supporting medium) involving oscillating electric and magnetic Üelds
at right angles to each other and to
the direction of propagation. In a vacuum the waves travel with a constant speed (the speed of light) of
2.9979 × 10
8 metres per second; if
material is present they are slower.
Alternatively, the energy can be regarded as a stream of *photons travelling at the speed of light, each
photon having an energy hc/λ, where
h is the Planck constant, c is the
speed of light, and λ is the wavelength of the associated wave. A fusion of these apparently conÛicting
concepts is possible using the methods of *quantum mechanics. The
characteristics of the radiation depend on its wavelength. See electromagnetic spectrum.
electromagnetic spectrum The
range of wavelengths over which
electromagnetic radiation extends.
The longest waves (10
5
–10
–3 metres)
are radio waves, the next longest
(10
–3 –10
–6 m) are infrared waves,
then comes the narrow band (4–7 ×
10
–7 m) of visible radiation, followed
by ultraviolet waves (10
–7 –10
–9 m)
and *X-rays and gamma radiation
(10
–9 –10
–14 m).
electromeric effect See electronic effects.
electrometallurgy The uses of
electrical processes in the separation
of metals from their ores, the reÜning of metals, or the forming or plating of metals.
electromotive force (e.m.f.) The
greatest potential difference that can
be generated by a particular source
of electric current. In practice this
may be observable only when the
source is not supplying current, because of its internal resistance.
electromotive series (electrochemical series) A series of chemical
elements arranged in order of their
*electrode potentials. The hydrogen
electrode (H
+ + e → ½H 2 ) is taken as
having zero electrode potential. Elements that have a greater tendency
than hydrogen to lose electrons to
their solution are taken as electropositive; those that gain electrons
from their solution are below hydrogen in the series and are called electronegative. The series shows the
order in which metals replace one
another from their salts; electropositive metals will replace hydrogen
from acids. The chief metals and hydrogen, placed in order in the series,
are: potassium, calcium, sodium,
magnesium, aluminium, zinc,
cadmium, iron, nickel, tin, lead,
hydrogen, copper, mercury, silver,
platinum, gold. This type of series is
sometimes referred to as an activity
series.
electron An elementary particle
with a rest mass of 9.109 3897(54) ×
10
–31 kg and a negative charge of
1.602 177 33(49) × 10
–19 coulomb.
Electrons are present in all atoms in
groupings called shells around the
nucleus; when they are detached
from the atom they are called free
electrolytic separation
196
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of separating isotopes by exploiting
the different rates at which they are
released in electrolysis. It was formerly used for separating deuterium
and hydrogen. On electrolysis of
water, hydrogen is formed at the
cathode more readily than deuterium, thus the water becomes enriched with deuterium oxide.
electromagnetic radiation Energy resulting from the acceleration
of electric charge and the associated
electric Üelds and magnetic Üelds.
The energy can be regarded as waves
propagated through space (requiring
no supporting medium) involving oscillating electric and magnetic Üelds
at right angles to each other and to
the direction of propagation. In a vacuum the waves travel with a constant speed (the speed of light) of
2.9979 × 10
8 metres per second; if
material is present they are slower.
Alternatively, the energy can be regarded as a stream of *photons travelling at the speed of light, each
photon having an energy hc/λ, where
h is the Planck constant, c is the
speed of light, and λ is the wavelength of the associated wave. A fusion of these apparently conÛicting
concepts is possible using the methods of *quantum mechanics. The
characteristics of the radiation depend on its wavelength. See electromagnetic spectrum.
electromagnetic spectrum The
range of wavelengths over which
electromagnetic radiation extends.
The longest waves (10
5
–10
–3 metres)
are radio waves, the next longest
(10
–3 –10
–6 m) are infrared waves,
then comes the narrow band (4–7 ×
10
–7 m) of visible radiation, followed
by ultraviolet waves (10
–7 –10
–9 m)
and *X-rays and gamma radiation
(10
–9 –10
–14 m).
electromeric effect See electronic effects.
electrometallurgy The uses of
electrical processes in the separation
of metals from their ores, the reÜning of metals, or the forming or plating of metals.
electromotive force (e.m.f.) The
greatest potential difference that can
be generated by a particular source
of electric current. In practice this
may be observable only when the
source is not supplying current, because of its internal resistance.
electromotive series (electrochemical series) A series of chemical
elements arranged in order of their
*electrode potentials. The hydrogen
electrode (H
+ + e → ½H 2 ) is taken as
having zero electrode potential. Elements that have a greater tendency
than hydrogen to lose electrons to
their solution are taken as electropositive; those that gain electrons
from their solution are below hydrogen in the series and are called electronegative. The series shows the
order in which metals replace one
another from their salts; electropositive metals will replace hydrogen
from acids. The chief metals and hydrogen, placed in order in the series,
are: potassium, calcium, sodium,
magnesium, aluminium, zinc,
cadmium, iron, nickel, tin, lead,
hydrogen, copper, mercury, silver,
platinum, gold. This type of series is
sometimes referred to as an activity
series.
electron An elementary particle
with a rest mass of 9.109 3897(54) ×
10
–31 kg and a negative charge of
1.602 177 33(49) × 10
–19 coulomb.
Electrons are present in all atoms in
groupings called shells around the
nucleus; when they are detached
from the atom they are called free
electrolytic separation
196
e
www.AzShimi.ir www.AzShimi.com