Inphase describes which condition?

• A. Out of phase by ninety degrees
• B. A state where waves cancel each other
• C. Applied to the condition that exists when two waves of the same frequency pass through their maximum and minimum values of like polarity at the same instant
• D. Inverted phase relation between waves

Answer: (C)

Inphase means two waves share the same frequency and have zero phase difference, so their peaks and valleys line up exactly. When both waves reach a maximum at the same instant, or both reach a minimum at the same instant, and they have the same polarity, they reinforce each other. That reinforcing, or constructive interference, is why this description fits inphase so well.

Other phase relationships describe different behavior: a ninety-degree difference is out of phase (quadrature), which doesn’t align peaks with peaks; opposite polarity at the same instant would be destructive interference, characteristic of a 180-degree phase shift.