Answer: 30 V.
- A 6 V
- B 42 V
- C 30 V
- D 21 V
Correct answer: C. 30 V
Explanation: The resistor and capacitor voltages are 90° out of phase. Therefore V = √(V<sub>R</sub><sup>2</sup> + V<sub>C</sub><sup>2</sup>) = √(24<sup>2</sup> + 18<sup>2</sup>) = 30 V.
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.