Answer: p(t) = v(t) × i(t).
- A p(t) = v(t) × i(t)
- B p(t) = Vrms × Irms
- C p(t) = V0 I0 / 2
- D p(t) = V0 I0
Correct answer: A. p(t) = v(t) × i(t)
Explanation: Instantaneous power = instantaneous voltage × instantaneous current. This varies with time. The average of this gives the mean power dissipated.
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.