If the pressure of the supply be, say 100 volts, the current would be 100 ÷ 31.8 = 3.14 amperes.
Fig. 1,288.—Pressure and current curves, illustrating lag. The effect of inductance in a circuit is to retard the current cycle, that is to say, if the current and pressure be in phase, the introduction of inductance will cause a phase difference, the current wave "lagging" behind the pressure wave as shown. In other words, inductance causes the current wave, indicated in the diagram by the solid curve, to lag behind the pressure wave, indicated by the dotted curve. Following the curves starting from the left end of the horizontal line, it will be noted that the current starts after the pressure starts and reverses after the pressure reverses; that is, the current lags in phase behind the pressure, although the frequency of both is the same.
Lag and Lead.—Alternating currents do not always keep in step with the alternating volts impressed upon the circuit. If there be inductance in the circuit, the current will lag; if there be capacity, the current will lead in phase. For example, fig. 1,288, illustrates the lag due to inductance and fig. 1,289, the lead due to capacity.
Ques. What is lag?
Ans. Lag denotes the condition where the phase of one alternating current quantity lags behind that of another. The term is generally used in connection with the effect of inductance in causing the current to lag behind the impressed pressure.
Fig. 1,289.—Pressure and current curves illustrating lead. The effect of capacity in a circuit is to cause the current to rise to its maximum value sooner than it would otherwise do; capacity produces an effect exactly the opposite of inductance. The phase relation between current and pressure with current leading is shown graphically by the two armature positions in full and dotted lines, corresponding respectively to current and pressure at the beginning of the cycle.
Ques. How does inductance cause the current to lag behind the pressure?