Answer: √(R² + (XL - XC)²).
- A √(R² + (XL - XC)²)
- B R + XL + XC
- C R + XL - XC
- D √(R² + XL² + XC²)
Correct answer: A. √(R² + (XL - XC)²)
Explanation: In series LCR, XL and XC are out of phase with each other. Z = √(R² + (XL - XC)²). When XL = XC, Z = R (resonance).
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.