Let an alternating voltage v = v sin ωt be applied across a pure resistance ‘R’. The applied voltage will be equal to the p.d across R at any instant of time t. Thus
Is the peak value of current in the circuit.
The above expression shows that in a pure resistance, the current is always in phase with the applied voltage.
The above graphical representation shows this. It shows that both v and i reach their zero, minimum and maximum values at the same time; there is thus no phase difference between v and i. The instantaneous power disipated in resistor is
The average value of P, over a complete cycle, is
