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18
SECTION 1
caesium
cesio
chemicals
sostanze chimiche
coil
spirale
magnetic field
campo magnetico
TECHNICAL ENGLISH
Friction
Conversion of
chemical energy
Thermal
emission
Doping of
semiconductors
Electromagnetism Photoelectricity
Ions
by rubbing
atoms with
net positive or
negative charges
examples:
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examples:
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by heating
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examples:
batteries and
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examples:
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3
Using the main points of the passage complete the chart below.
2
Read the passage below and identify the main points, underlying the sentences that convey main
ideas.
Sources of electricity
T
here are electrons and protons in the atoms of all
materials, but to do useful work these charges
must be separated in order to produce a potential
difference that will create a flow, a current.
Some of the more common methods of producing
electricity are:
1.
Friction
produces static electricity. In an
insulator electrons can be separated by rubbing
which produces opposite charges that remain in
the dielectric.
2.
Conversion of chemical energy.
Chemicals
are used in both wet and dry cells and batteries.
The chemical reaction produces opposite charges
on two dissimilar metals which function as the
positive and negative terminals.
3.
Ions.
Atoms can be made to gain or lose orbital
electrons either through a chemical reaction or
through the electric field of an applied voltage.
Such atoms with a net charge are called ions.
These ion charges can be either positive or
negative. Ions, generally, provide ionization
currents in liquids and gases.
4.
Electromagnetism.
Electricity and magnetism
are closely related. Any moving charge has a
magnetic field, which can produce current: the
magnetic field
will be in a plane perpendicular
to the current. The magnetic field of any current
is the basis of many electromagnetic applications,
including magnets, relays, loudspeakers,
transformers and
coils
in general. An electric
motor is one example of the use of a coil.
A generator produces voltage by means of a
conductor rotating in a magnetic field.
5.
Photoelectricity.
Some materials can emit electrons
when light strikes
1
their surfaces. For example:
caesium
.
6.
Thermal emission.
When materials are heated
they can throw electrons off
2
from their surfaces.
7.
Doping of semiconductors:
for example,
germanium and silicon can be changed from
the inert condition by adding small amounts of
an ‘impure’ element. This technique of adding
charges to a semiconductor is called doping.
1
light strikes
: light hits/reflects off
2
throw something off
: propel with force
TEXT 1
Progetto FOR ELECTRONICS_unit_1.indd 18
10/01/