ELECTRONIC PRINCIPLES - OD1647 - LESSON 1/TASK 1
through the resistor on its way to the capacitor. At time to,
the current flowing to the capacitor is maximum. Thus, the
voltage drop across the capacitor is maximum (E=IR). As time
progresses toward time t1, the current flowing to the capacitor
steadily decreases and causes the voltage developed across the
resistor (R) to steadily decrease. When time t1 is reached,
current flowing to the capacitor is stopped, and the voltage
developed across the resistor has decreased to zero.
It should be remembered that capacitance opposes a change in
voltage. This is shown by comparing figure 34, graph A to graph
D, on the previous page. In graph A, the voltage changed
instantly from 0 volts to 6 volts across the circuit., while the
voltage developed across the capacitor in figure 34, graph D
took the entire time interval from to to time t1 to reach 6
volts. The reason for this is that In the first instant at time
to, maximum current flows through R and the entire circuit
voltage is dropped across the resistor. The voltage impressed
across the capacitor at to is zero volts. As time progresses
toward t1, the decreasing current causes progressively less
voltage to be dropped across the capacitor (C). At time t1, the
voltage across the capacitor is equal to the source voltage (6
volts), and the voltage dropped across the resistor (R) is equal
to zero. This is the complete charge cycle of the capacitor.
As may have been noticed, the processes which take place in the
opposite to those in a series LR circuit.
For comparison, the important points of the charge cycle of RC
and LR series circuits are summarized in table 1 on the
following page.
capacitor is fully charged. When S1 is open and S2 closes, the
capacitor discharge cycle starts. At the first instant, circuit
voltage attempts to go from source potential (6 volts) to zero
volts, as shown in figure 35, graph A. Remember, though, the
capacitor during the charge cycle has stored energy in an
electrostatic field.
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