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3-30
source voltage and the action stops (view D). As each capacitor is charged, current in each inductor drops
to zero, effectively reflecting the current with the opposite polarity (view C). Reflected current of
opposite polarity cancels the original current at each point, and the current drops to zero at that point.
When the last capacitor is charged, the current from the source stops flowing (view D).
Important facts to remember in the reflection of dc voltages in open-ended lines are:
Voltage is reflected from an open end without change in polarity, amplitude, or shape.
Current is reflected from an open end with opposite polarity and without change in amplitude or
shape.
REFLECTION OF DC VOLTAGE FROM A SHORT CIRCUIT
A SHORT-CIRCUITED line affects voltage change differently from the way an open-circuited line
affects it. The voltage across a perfect short circuit must be zero; therefore, no power can be absorbed in
the short, and the energy is reflected toward the generator.
The initial circuit is shown in figure 3-25, view A. The initial voltage and current waves (view B) are
the same as those given for an infinite line. In a short-circuited line the voltage change arrives at the last
inductor in the same manner as the waves on an open-ended line. In this case, however, there is no
capacitor to charge. The current through the final inductor produces a voltage with the polarity shown in
view C. When the field collapses, the inductor acts as a battery and forces current through the capacitor in
the opposite direction, causing it to discharge (view D). Since the amount of energy stored in the
magnetic field is the same as that in the capacitor, the capacitor discharges to zero.
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