What characterizes out-of-phase waves?

• A. Peaks and troughs occur at different times.
• B. Peaks and troughs occur at the same times.
• C. Amplitude increases
• D. Wavelength doubles.

Answer: (A)

Out-of-phase waves have a phase difference between them, so their peaks and troughs do not line up in time. When one wave reaches a maximum, the other is shifted, so its crest occurs at a different moment (for example, when one is at a peak, the other might be at a zero crossing or a trough). This timing offset is what defines the out-of-phase relationship. Amplitude and wavelength are separate properties and don’t by themselves describe the phase relationship; two waves can be out of phase yet have the same amplitude and wavelength, leading to different interference outcomes.