ELECTRONIC PRINCIPLES - OD1647 - LESSON 1/TASK 1
dielectric material in a practical capacitor is not perfect and
a small leakage of current will flow through the dielectric.
This current will eventually dissipate the charge. However, a
high quality capacitor may hold its charge for a month or more.
FIGURE 33. DISCHARGING A CAPACITOR.
To review briefly, when a capacitor is connected across a
voltage source, a surge of charging current flows. This
charging current develops a cemf across the capacitor which
opposes the applied voltage. When the capacitor is fully
charged, the cemf is equal to the applied voltage and charging
current ceases. At full charge, the electrostatic field between
the plates is at maximum intensity and the energy stored in the
dielectric is maximum. If the charged capacitor is disconnected
from the source, the charge will be retained for some period of
time. The length of time the charge is retained depends on the
amount of leakage current present. Since electrical energy is
stored in the capacitor, a charged capacitor can act as a source
emf.
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