AC circuit containing pure resistor
Consider a circuit containing a pure resistor of resistance R connected across an alternating voltage source (Figure 4.45). The instantaneous value of the alternating voltage is given by
An alternating current i flowing in the circuit due to this voltage, develops a potential drop across R and is given by
Kirchoff’s loop rule (Refer section 2.4) states that the algebraic sum of potential differences in a closed circuit is zero. For this resistive circuit,
where Vm/R = Im , the peak value of alternating current in the circuit. From equations (4.43) and (4.45), it is clear that the applied voltage and the current are in phase with each other in a resistive circuit. It means that they reach their maxima and minima simultaneously. This is indicated in the phasor diagram (Figure 4.46). The wave diagram also depicts that current is in phase with the applied voltage (Figure 4.46).