Opposite-Direction Superposition for Stationary Waves

Steps:

• Identify that stationary waves form via interference of two progressive waves.
• Recall the superposition principle: waves must have equal frequency, amplitude, and phase for standing patterns.
• Note that opposite directions ensure phase differences create fixed nodes and antinodes.
• Confirm same-direction waves reinforce to form another progressive wave, not stationary.

Why C is correct:

• Stationary waves arise when two coherent waves of equal frequency travel in opposite directions, as per the superposition principle, producing zero net propagation.

Why the others are wrong:

• A: Wave type (longitudinal or transverse) is irrelevant; stationary waves form in both via opposite-direction interference.
• B: Identical to C, but question specifies C as correct; opposite directions are key regardless.
• D: Same-direction waves superpose to create a resultant progressive wave with altered amplitude, not stationary.

Final answer: C