Answer / prosenjit majumder

In a DC circuit the power is the product of current and
voltage . Because in a DC circuit current and voltag
waveform always in a same phase . But in a AC circuit the
current and voltage may not be always in same phase .
Depending upon load (either inductive or capacitive ),
current and voltage waveform varies from each other. If
load is resistive then power is denoted by watt. If load is
capacitive or inductive then it is denoted by va .Here
power factor does matter .

Answer / loki

in dc average values of voltage and currents are always
constant.in ac instantaneous values differ from time to
time so we will take rms values

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