Sound waves cause longitudinal motion in air molecules

Steps:

• Sound waves are longitudinal, meaning molecules vibrate parallel to the wave's propagation direction.
• A loudspeaker produces compressions and rarefactions that push-pull molecules along this axis.
• At point P, the molecule oscillates back and forth in the direction of wave travel, matching the 200 Hz frequency.
• Diagram A depicts this linear, parallel displacement.

Why A is correct:

• Longitudinal waves, by definition, involve particle motion parallel to propagation, as per wave mechanics.

Why the others are wrong:

• B shows transverse motion perpendicular to propagation, incorrect for sound in air.
• C depicts circular or elliptical paths, not applicable to linear sound vibrations.
• D illustrates radial or no displacement, ignoring the oscillatory nature of sound.

Final answer: A