Final answer:
In a balanced 3-phase system, the phases are spaced exactly 120 degrees apart for efficient operation. Two sine waves with a 180-degree phase difference and equal amplitude traveling in the same direction will have a resultant amplitude of zero due to destructive interference.
Step-by-step explanation:
A balanced 3-phase system has its phases spaced exactly 120 degrees apart. This phase difference ensures that the three-phase system operates efficiently and can provide continuous power. In such a system, when one phase reaches its peak voltage, the other two phases are one-third of a cycle away from their peaks, maintaining a stable and balanced power supply.
Regarding the additional question about sine waves, when two sine waves that have the same amplitude (A) and are 180 degrees out of phase travel in the same direction in a medium, they cancel each other out. This phenomenon is due to destructive interference, where the peak of one wave aligns with the trough of another, resulting in a resultant amplitude of zero.