The resistor, the capacitor and the coil all oppose the flow of ac current. Their combined opposition is called impedance, Z. Ohm's Law can be applied, as shown in the top formula. The higher the impedance, the lower the current.
The resistor has resistance. The capacitor has capacitive reactance. The coil has inductive reactance. All of these values are measured in ohms. However, impedance is not calculated by adding these values.
The bottom formula must be used.
If you are familiar with Pythagoras, this is another application of it.
When
coupling
one
device
to
another,
such as
an
amplifier
to a
loudspeaker,
the
output
impedance
of the
amplifier
and
the
input
impedance
of the
speaker
must be
the
same, to
give
optimum
transfer
of power
from one
to the
other. |