A pair of waves are considered in-phase when their peaks occur at the same time and at the same location.

A pair of waves are considered in-phase when their peaks occur at the same time and at the same location.

• A. In-phase
• B. Out-of-phase
• C. Phase-locked
• D. Coherent

Answer: (A)

In-phase means the waves share the same phase, so their peaks line up in time and space. When crests align with crests and troughs with troughs, their amplitudes add constructively to produce a larger resultant wave. That exact alignment—peaks occurring at the same time and at the same location—is what defines being in-phase. Out-of-phase describes a half-cycle offset, so a crest in one wave aligns with a trough in the other, leading to destructive interference. Phase-locked refers to a fixed phase relationship, but the constant offset can be nonzero, so peaks don’t have to coincide in space. Coherent means a constant phase relationship and the same frequency, but this can include a nonzero phase difference as well; coherence doesn’t require the peaks to line up at the same place and time.

In-phase means the waves share the same phase, so their peaks line up in time and space. When crests align with crests and troughs with troughs, their amplitudes add constructively to produce a larger resultant wave. That exact alignment—peaks occurring at the same time and at the same location—is what defines being in-phase.

Out-of-phase describes a half-cycle offset, so a crest in one wave aligns with a trough in the other, leading to destructive interference. Phase-locked refers to a fixed phase relationship, but the constant offset can be nonzero, so peaks don’t have to coincide in space. Coherent means a constant phase relationship and the same frequency, but this can include a nonzero phase difference as well; coherence doesn’t require the peaks to line up at the same place and time.