文档介绍：Reading 13 Ron Bertrand VK2DQ
CAPACITIVE REACTANCE
CAPACITOR IN A DC CIRCUIT
We have already discussed the operation of a capacitor in a DC circuit, however let's just
go over the main principles again.
If a capacitor is connected to a battery (or other DC source) it will charge according to its
time constant (T=CR), to the battery voltage. If a lamp were connected in series with the
capacitor while it was charging, the lamp would give off light indicating that current was
flowing. The lamp would be bright at first and then slowly dim to nothing as the capacitor
charged. Current into the charging capacitor is high at first and then tapers off to zero
when it is charged. The voltage on the capacitor is low at first and increases to the supply
voltage when the capacitor is charged. We can see that the voltage across, and the
current into a capacitor, are not in sync (phase). Current in a capacitive circuit leads the
voltage (by 90 degrees).
Imagine a capacitor and a lamp in series. Connect the circuit to a DC source and the lamp
will light momentarily as described in the last paragraph. The capacitor is now charged and
the lamp is out. Suppose now we reverse the battery (or supply terminals). The capacitor
will now discharge through the lamp and the battery, and then recharge with the opposite
polarity.
Imagine now c