alleryStart learning →A purely RESISTIVE AC load has voltage and current that are
Ain phase ($\phi = 0$)
B90 degrees out of phase
C180 degrees out of phase
Dalways at right angles
Answer & Solution
Correct answer: A. in phase ($\phi = 0$)
1. PURE RESISTOR: Ohm's law $v = iR$ holds INSTANTANEOUSLY.
2. So if $v(t) = V_m\sin(\omega t)$, then $i(t) = (V_m/R)\sin(\omega t)$ — SAME phase.
3. Phase difference $\phi = 0$ → power factor $\cos(0) = 1$.
4. All energy delivered to a pure resistor is REAL POWER — heat dissipated.
5. Other options apply to inductors (90° lag), capacitors (90° lead), or opposite polarity.
_Source: Tony Kuphaldt, "Lessons in Electric Circuits — AC", Vol II, Ch 2 (Resistor AC behavior)._
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