Destructive Interference from 180° Phase Difference

Steps:

• The two waves from S1 and S2 reach P with equal amplitude x0.
• The 180° phase difference means one wave is inverted relative to the other.
• At P, the waves are out of phase, causing their displacements to cancel.
• Resulting amplitude is the vector sum: x0 + (-x0) = 0.

Why A is correct:

• Superposition principle states that waves with equal amplitude and 180° phase difference interfere destructively, yielding zero amplitude.

Why the others are wrong:

• B: x/2 assumes partial interference, but full cancellation occurs here.
• C: x0 ignores the second wave's opposing effect.
• D: 2x0 applies to constructive interference with 0° phase difference.

Final answer: A