Final answer:
AC RMS power and DC power are not equal because DC is constant, while AC alternates and must use RMS values for comparison. RMS values in AC circuits are used to find equivalent DC values for power calculations.
Step-by-step explanation:
AC RMS power and DC power are not equal. Direct Current (DC) is the constant flow of electric charge in one direction, whereas Alternating Current (AC) is the flow of electric charge that reverses direction periodically. In AC, voltage and current are sinusoidal and can differ in phase. For AC to be compared to DC, RMS (Root Mean Square) values are used, which are a form of average that allows us to relate AC to an equivalent DC value.
The RMS voltage and RMS current are the square roots of the mean (average) of the squares of the instantaneous values. The average power in an AC circuit, for a purely resistive load where voltage and current are in phase, is given by Pave = Irms × Vrms. In contrast, DC power can be calculated simply by multiplying the constant voltage by the constant current.
AC power is used for power transmission because it can be easily transformed to other voltages and transported over long distances with less loss as compared to DC power. Most household electricity is an example of AC power, quoted as 120 V AC, which refers to the RMS voltage.