What is the effect of constructive interference on the amplitude of the resultant wave?

• A. The resultant wave is larger.
• B. The resultant wave is smaller.
• C. There is no change in the resultant wave.
• D. The frequency doubles.

Answer: (A)

Constructive interference happens when two waves meet in phase, so their displacements add together. The peaks line up with peaks and the troughs with troughs, making the resulting wave’s amplitude equal to the sum of the two amplitudes at each point. That means the resultant amplitude is larger than either wave alone—potentially as large as the sum of their amplitudes if they have the same phase and similar sizes. The frequency, however, comes from the source waves and does not change just because the waves interfere. So the correct idea is that the amplitude increases due to in-phase addition, while the frequency remains the same.