The Basics of Resistance and Impedance

Introduction:
When working with electrical circuits, it is essential to understand two fundamental concepts: resistance and impedance. While both refer to opposition to current flow, they differ in terms of how they behave in an AC (Alternating Current) circuit versus a DC (Direct Current) circuit.

Resistance:
Resistance is the opposition to current flow in a circuit and is most commonly associated with DC circuits. It is a property of materials that impedes the movement of electrons. The unit of resistance is Ohms (Ω). In a DC circuit, the resistance is constant and does not change with time, as there is no variation in voltage or current direction.

Impedance:
Impedance, on the other hand, refers to the total opposition to current in an AC circuit. It combines both resistance (real component) and reactance (imaginary component), which accounts for the opposition due to capacitors and inductors in the circuit. The unit of impedance is also Ohms (Ω), but unlike resistance, impedance changes with frequency.

Key Differences:
1. Type of Circuit:
Resistance applies to DC circuits. Impedance applies to AC circuits.

2. Components:
Resistance only depends on the material, temperature, and geometry of the conductor. Impedance depends on resistance, capacitance, and inductance, and is affected by the frequency of the current.

3. Behavior:
Resistance is constant. Impedance varies with frequency.

Conclusion:
While resistance and impedance are both measured in Ohms and represent opposition to current, impedance extends the concept of resistance by incorporating frequency-dependent factors like capacitance and inductance in AC circuits.