the voltage across either L or C is equal to the large circulating current times
reactance, the voltage developed can be very large.
In fact, if R is low, the
voltage developed across the tuned circuit may be equal to the applied voltage E.
At this time, current drawn from the generator (line current) will drop to nearly
zero. Thus we say that the impedance of a parallel-tuned circuit at resonance is
maximum.
e. The line current flowing to the parallel-tuned circuit in A of Figure 26
can be measured by meter Al.
If the source frequency is varied from a low
frequency through the resonant frequency to a high frequency, the line current will
rapidly decrease from its highest value at the low frequency to a minimum at the
resonant frequency, and will then rise again to a high value at the high frequency.
The current characteristic of this circuit is shown in B of Figure 26. This graph
either side of the resonant frequency.
f. Selectivity and sensitivity of a parallel-tuned circuit are determined to
a large extent by the amount of resistance in the inductor. This characteristic is
similar for both series-tuned and parallel-tuned circuits. The characteristics of
a parallel-tuned circuit at resonance can be summed up as follows:
(1) Circulating current around the loop of L, C, and R is maximum.
(2) Line current from the generator is minimum.
(3) Impedance presented to the generator is maximum.
LESSON EXERCISES
In each of the following exercises, select the ONE answer that BEST completes
the statement or answers the question.
Indicate your solution by circling the
letter opposite the correct answer in the subcourse booklet.
1.
Two of the particles that make up an atom carry electrical charges.
These particles are
a.
neutrons and protons.
c.
protons and molecules.
b.
protons and electrons.
d.
electrons and neutrons.
2.
All substances will pass electric current to some extent, but certain
substances pass it more easily than others.
Electrical current will flow more
easily through copper than through glass because, compared with glass, copper has
a.
higher resistance.
c.
more free neutrons.
b.
lower conductivity.
d.
more free electrons.
308
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