What term describes two sine waves that are completely aligned with each other?

The term that describes two sine waves that are completely aligned with each other is "in phase." When two sine waves are in phase, their peaks, troughs, and zero-crossings occur at the same time. This means that they synchronize perfectly, ensuring that, at any given moment, the amplitudes of the waves correspond directly to each other. As a result, if you were to combine these waves, you would see an increase in amplitude due to constructive interference, where the waves reinforce each other.

Understanding this concept is critical in fields such as physics and engineering, where wave behavior plays a significant role in the analysis of sound, light, and other wave phenomena. Being in phase leads to coherent wave patterns, which can be essential in applications like signal processing and telecommunications.