(1) The internal construction
of a paper capacitor is
illustrated in A of figure
20
with
the
physical
appearance of some types
shown in B of that figure.
The "pigtails" of wire or
terminals
of
the
capacitors are fastened to
the sheets of conducting
material.
(2) Representative
types
of
mica
and
ceramic
capacitors,
electrolytic
capacitors, and variable
capacitors
are
shown
respectively in A, B, and
C of figure 21.
The
plates of the rotor, or
movable
element
of
a
tuning type of variable
capacitor,
slides
in
between the plates of the
stator.
These plates are
separated by air serving
as the dielectric.
(3) Examples
of
schematic
symbols for capacitors can
be seen in figure 22.
Figure 20. Paper capacitors.
From the symbol, it is not
possible to determine the
type of dielectric used.
The only distinguishable
feature
is
that
the
capacitor is either fixed
or variable.
Sketch A
indicates
a
fixed
capacitor.
Sketch
B
indicates a variable capacitor. Sketch C shows two variable capacitors
which are tuned by the same control knob.
When this occurs, the
capacitors are said to be ganged and may be located in different
circuits.
Generally the largest capacitors are used in the power
supply since they operate at power frequencies.
The next largest are
in the audio circuits. The capacitors used in radio-frequency circuits
are generally small in comparison with those used at lower frequencies.
14.
OPERATION OF INDUCTORS IN AC CIRCUITS
a. Counter Electromotive Force. As stated previously. In ac circuits there
is an opposition to the flow of current besides the resistance of the circuit.
This additional opposition is caused by the back or counter electromotive force, so
named to distinguish it from the applied voltage, which is the original force
tending to set up a current flow.
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