Understanding Total Opposition in AC
Impedance ($Z$) is the total opposition that a circuit presents to alternating current (AC). While resistance only measures opposition to the flow of electrons, impedance includes Reactance ($X$), which measures opposition due to the storage of energy in electric or magnetic fields.
Resistance vs. Reactance
- Resistance ($R$): Purely "frictional". It stays in phase with the voltage and converts energy into heat.
- Reactance ($X$): Purely "reactive". It causes a phase shift between voltage and current. Energy is stored temporarily and then returned to the circuit.
Impedance is a vector quantity. You cannot simply add resistance and reactance together; they must be combined using the Pythagorean theorem, as they act at $90^\circ$ to each other in the complex plane.
The Formula
Where:
Z=
Total Impedance magnitude (Ohms)R=
Resistance (Ohms)X=
Total Reactance (Ohms)Example Calculation
A loudspeaker has a resistance of $6 , \Omega$ and an inductive reactance of $8 , \Omega$ at a specific audio frequency.
- Apply Pythagorean Theorem: $\sqrt{6^2 + 8^2} = \sqrt{36 + 64} = \sqrt{100} = 10 , \Omega$.
The total impedance is $10 , \Omega$.