Answer: 0.5 A.
- A 0.5 A
- B 2 A
- C 60 A
- D 120 A
Correct answer: A. 0.5 A
Explanation: P = V<sub>rms</sub> × I<sub>rms</sub> × cos(φ). For pure resistive bulb, cos(φ) = 1. I<sub>rms</sub> = P/V<sub>rms</sub> = 60/120 = 0.5 A.
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.