Question 3-12B6

To determine the phase relationship between two signals, observe which signal reaches a specific point in its cycle (such as the positive-going zero crossing or its peak voltage) *earlier* in time. The signal that reaches that point earlier is said to "lead," while the signal that reaches it later is said to "lag." In Figure 3B3 (as typically presented for this question), signal A completes its positive-going zero crossing (or reaches its positive peak) exactly one-quarter of a cycle *before* signal B reaches the same point. Since one full cycle represents 360 degrees, one-quarter of a cycle is 90 degrees. Because signal B's cycle is delayed relative to A's by this amount, B is *lagging* A by 90 degrees. Therefore, option B accurately describes this relationship. Option A is incorrect because A is earlier, not later. Options C and D describe different phase shifts or the wrong leading/lagging relationship.