What is phase?

• A. The time delay between two signals
• B. The amplitude difference between signals
• C. The speed of a wave
• D. The relationship between two signals that share the same frequency

Answer: (D)

Phase is the relationship between two signals that share the same frequency. When two sinusoids have the same ω, you can describe one as x1(t) = A cos(ωt) and the other as x2(t) = B cos(ωt + φ). The phase difference φ tells you how far one wave is shifted in time relative to the other. If φ = 0, they peak together (in phase); if φ is nonzero, one leads or lags by a fraction of a cycle. A time delay Δt creates a phase shift φ = ωΔt for that frequency, so delay and phase are linked, but phase itself is specifically about the relative alignment of cycles, not the speed or amplitude of the wave.