Answer: 2πfL.
- A 2πfL
- B 2πf/L
- C L/(2πf)
- D 1/(2πfL)
Correct answer: A. 2πfL
Explanation: X<sub>L</sub> = ωL = 2πfL (in ohms). X<sub>L</sub> increases with frequency, so inductors block high-frequency AC but allow DC through easily.
In a pure inductor the current lags the voltage by 90° (energy is briefly stored in the magnetic field before current responds); in a pure capacitor the current leads the voltage by 90° (current must flow to build up charge before voltage rises) - the mnemonic "ELI the ICE man" keeps these straight.
Concept context
AC circuits, impedance, LCR series circuit, resonance, transformers, and power factor.