Ohm's Law for AC Circuits
The familiar Ohm's Law triangle used for DC circuits can only be used at AC if the load is
purely resistive. In most ac circuits however, the load or input or output is a combination of resistance, capacitance
and / or inductance. The general term is impedance and given the symbol Z. The current flow in an ac circuit is no
longer in phase with the voltage ( as it would be at dc ) and will either lead or lag the
voltage. The impedance triangle is shown below:
The triangle isa used exactly the same as Ohm's Law at DC except that impedance now replaces resistance. It should be noted
that when measuring ac voltages or currents, your meter will only indicate correct values over a limited frequency range.
This is usually valid from DC up to 400Hz but can be found by checking the specifications
for your meter.
