Wirkwiderstand

Wirkwiderstand, in the context of alternating current (AC) circuits, denotes the real part of the complex impedance. The impedance Z of a network is generally written as Z = R + jX, where R is the Wirkwiderstand and X is the reactance (due to inductors and capacitors). R represents the portion of impedance that dissipates energy as heat and is measured in ohms (Ω). The imaginary part X accounts for energy storage rather than dissipation.

The magnitude of impedance is |Z| = sqrt(R^2 + X^2) and the phase angle is φ = arctan(X/R). The real power delivered to the circuit is P = I_rms^2 R = V_rms^2 R / |Z|^2 = V_rms I_rms cosφ, where cosφ = R/|Z| is the power factor. Thus, the Wirkwiderstand determines how much of the input power is converted to heat, independent of the reactive energy exchanged with the circuit.

Physically, R reflects resistive losses arising from material resistivity, geometry, temperature, and contact resistance. X arises from energy storage in magnetic and electric fields. In a pure resistor, X = 0 and Z = R. In real components, parasitic inductance and capacitance cause nonzero X, so no component is a perfect resistor across all frequencies.

Applications of the concept include circuit analysis, impedance matching, and power calculations in AC networks. Understanding the Wirkwiderstand helps engineers predict dissipation, heating, and the effectiveness of energy transfer in electrical systems.