Resultant Displacement for Two Waves in Antiphase

Problem

Two waves of equal amplitude overlap at a point. At one instant, one contributes +2.0 mm displacement and the other contributes -2.0 mm. Find the resultant displacement.

Solution

Apply superposition:

$y=y_1+y_2=(+2.0)+(-2.0)=0\mathrm{mm}$

The point is momentarily at equilibrium because the displacements cancel.

Common Mistakes

• Adding amplitudes instead of instantaneous displacements
• Assuming cancellation means the waves disappear

Links

• Related: superposition
• Misconception: interference changes frequency