AC Reactance: The Same Inductor or Capacitor Changes Its Opposition with Frequency

Name the AC quantity

For ideal sinusoidal analysis, inductive reactance is 2πfL and capacitive reactance is 1/(2πfC). They have opposite frequency dependencies. Primary reference: reactance.

Reactance uses ohms but does not represent the same mechanism as a DC resistive voltage drop. Keep its reactive sign or phase convention when it enters a complete impedance calculation. Actual components can include resistance and other frequency-dependent behavior.

An invented frequency comparison

Choose fictional L =10 mH and C =10 µF. At 100 Hz, the ideal inductive reactance is approximately 6.283 Ω, while the capacitive magnitude is approximately 159.15 Ω. At 1,000 Hz, those magnitudes become 62.83 Ω and 15.915 Ω.

Increasing frequency tenfold increases the first magnitude tenfold and divides the second by ten. Adding these magnitudes directly as though both were resistors would discard their opposing reactive character. The numbers specify no filter circuit or installed drive component.

Preserve the interpretation basis

Prepare columns for frequency, inductance, capacitance, assumed resistance and the intended impedance model. State whether the signal is sinusoidal or needs analysis of multiple frequency components.

Request component behavior under the relevant conditions before applying the ideal relation to an actual assembly. This worksheet helps explain why one component label can accompany different AC behavior without being a change in its nominal inductance or capacitance.

Customer Questions

Primary References

These references support the technical principles discussed in this guide. The worked examples and review questions are educational.

• Primary reference: reactance