English: Diagram showing a voltage waveform and the corresponding power waveform (dissipated by a resistive load).

The power is zero when the voltage is zero. Otherwise, the power waveform is always positive, as the resistor can only dissipate energy; it cannot supply energy to the circuit. In other words, the resistor outputs power regardless of whether the voltage is positive or negative.

• The RMS voltage is shown by the blue line. ${\displaystyle V_{\mathrm {rms} }={\frac {V_{\mathrm {pk} }}{\sqrt {2}}}}$
• The peak power is shown by the red line. ${\displaystyle P_{\mathrm {pk} }={\frac {{V_{\mathrm {pk} }}^{2}}{R}}}$
• The average power is shown by the green line. ${\displaystyle P_{\mathrm {avg} }={\frac {P_{\mathrm {pk} }}{2}}={\frac {{V_{\mathrm {rms} }}^{2}}{R}}}$