Question

For a sound wave in air, the vibrations of the particles of a medium :

• A. Are parallel to the direction of propagation
• B. Are perpendicular to the direction of propagation
• C. May either be parallel or perpendicular to the direction of propagation
• D. None of the above

Answer 1

The correct option is A Are parallel to the direction of propagation

Answer is A.
Sound is a mechanical wave that results from the back and forth vibration of the particles of the medium through which the sound wave is moving. If a sound wave is moving from left to right through air, then particles of air will be displaced both rightward and leftward as the energy of the sound wave passes through it. The motion of the particles is parallel to the direction of the energy transport. This is what characterizes sound waves in air as longitudinal waves.