Resistance vs. Impedance: Key Differences Explained

This article clarifies the fundamental differences between resistance and impedance. The following table provides a comprehensive comparison of these two important concepts.

Resistance vs. Impedance: A Detailed Comparison

| Feature | Resistance | Impedance | | -------------------------------- | -------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------ | --- | ------------------------------- | | Definition | Opposition to the flow of DC (Direct Current). | Opposition to the flow of AC (Alternating Current). | | Unit of Measurement | Ohm (Ω) | Ohm (Ω) | | Measurement Tool | Ohmmeter or Multimeter | Impedance Meter | | Circuit Symbol | ‘R’ | ‘Z’ | | Formula | | $Z = R + jX$ (Cartesian Form), $Z = | Z | e^{j\cdot arg(z)}$ (Polar Form) | | Inverse | Conductance (G), $G = \frac{1}{R}$ | Admittance (Y), $Y = \frac{1}{Z}$ | | Frequency Dependence | Does not depend on frequency. However, the resistance of the material varies with temperature. | Depends on frequency. | | Ohm’s Law | $R = \frac{V}{I}$ | | | Special Cases & Phase Angles | | $Z = R$, Phase angle = 0°
$Z = X_L = \omega L$, Phase angle = 90°
$Z = X_C = \frac{1}{\omega C}$, Phase angle = -90° | | R-L Circuit | | $Z = \sqrt{R^2 + (X_L)^2}$, $0° < \phi < 90°$ | | R-C Circuit | | $Z = \sqrt{R^2 + (X_C)^2}$, $-90° < \phi < 0°$ | | R-L-C Circuit | | $Z = \sqrt{R^2 + (X_L - X_C)^2}$ |

Key Takeaways:

• Resistance is a constant opposition to DC current, while Impedance is a frequency-dependent opposition to AC current.
• Impedance considers both resistance and reactance (opposition due to inductors and capacitors).
• The phase angle in impedance represents the phase difference between voltage and current in an AC circuit.