Which best describes the motion of air particles when a sound wave passes through them? a. the particles move together and apart perpendicular to the direction of the wave. b. air particles move parallel to the sound waves c. the particles move perpendicular to the direction of the wave. d. the particles move both perpendicular and parallel to the direction of the wave.

Before solving this question first we have to understand longitudinal wave and transverse wave.

A longitudinal wave is a wave in which the particles of the medium vibrate parallel to the direction of propagation of wave. In this type of wave one will notice compressions and rarefactions. Compressions are  high  pressure zones where the particles of the medium are close to each other . The rarefactions are low pressure zones where  there will be  large separation between particles.

A longitudinal wave is a repeated motion of compressions and rarefactions. The particle of the medium show a little displacement along the direction of wave.

A transverse wave is a wave in which the particle vibration is perpendicular to the direction of propagation of wave .In this type of wave one will notice crests and troughs.It is a repeated motion of crests and troughs.

Sound wave is a longitudinal wave. When it passes through  air it forms rarefactions and compressions.

Hence from the above we get that out of the four options given in the question only option B is right which depicts that the air particles move parallel to the sound waves.

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