Stationary waves from wave reflection and interference

Steps:

• Stationary waves form when two coherent waves of same frequency travel in opposite directions and interfere.
• Evaluate A: Blowing over bottle creates air vibrations that reflect inside, forming nodes and antinodes.
• Evaluate B: Sound reflection creates echo, but waves remain traveling, not stationary.
• Evaluate C: Double slit causes interference of light waves, producing pattern but no standing waves.
• Evaluate D: Narrow slit diffracts water waves, spreading them without opposition for stationary formation.

Why A is correct:

• It excites resonance in a closed air column, where incident and reflected waves superpose per the principle of superposition, creating stationary waves with fixed nodes.

Why the others are wrong:

• B: Generates a delayed reflected wave (echo), but no sustained opposition for stationary pattern.
• C: Produces traveling wavefront interference fringes, not fixed stationary waves.
• D: Causes wave bending and spreading via diffraction, resulting in propagating waves only.

Final answer: A