frequencies the current changes more rapidly than it does at lower frequencies.On the other hand,the inductive reactance vanishes as approaches zero. By comparing Eq.(12.2.14)to Eq.(12.1.2),we also find the phase constant to be (12.2.17) The current and voltage plots and the corresponding phasor diagram are shown in the Figure 12.2.4 below. I() Figure 12.2.4 (a)Time dependence of I(t)and V(t)across the inductor.(b)Phasor diagram for the inductive circuit. As can be seen from the figures,the current I(t)is out of phase with V(t)by =z/2; it reaches its maximum value after V(t)does by one quarter of a cycle.Thus,we say that The current lags voltage by /2 in a purely inductive circuit 12.2.3 Purely Capacitive Load In the purely capacitive case,both resistance R and inductance L are zero.The circuit diagram is shown in Figure 12.2.5. Vc(t) V(t)=Vosin@t Figure 12.2.5 A purely capacitive circuit 12-7frequencies the current changes more rapidly than it does at lower frequencies. On the other hand, the inductive reactance vanishes as ω approaches zero. By comparing Eq. (12.2.14) to Eq. (12.1.2), we also find the phase constant to be 2 π φ = + (12.2.17) The current and voltage plots and the corresponding phasor diagram are shown in the Figure 12.2.4 below. Figure 12.2.4 (a) Time dependence of ( ) L I t and ( ) VL t across the inductor. (b) Phasor diagram for the inductive circuit. As can be seen from the figures, the current ( ) L I t is out of phase with ( ) by VL t φ = π / 2 ; it reaches its maximum value after ( ) does by one quarter of a cycle. Thus, we say that VL t The current lags voltage by π / 2 in a purely inductive circuit 12.2.3 Purely Capacitive Load In the purely capacitive case, both resistance R and inductance L are zero. The circuit diagram is shown in Figure 12.2.5. Figure 12.2.5 A purely capacitive circuit 12-7