A sound wave is a pressure wave in the sense that it has regions of high pressure (compressions) and low pressure (rarefactions) which were established due to the vibrations of the sound source. Justify why these compressions and rarefactions occur.

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Sound is denser than air and has more inertia, resulting in the bouncing up of sound.

The speed of the sound waves only depends on the properties of the medium.

Sound like all waves, can bend into the regions of space behind obstacles.

Sound can reflect off fixed ends and interfere with incident waves, and vibrates longitudinally. The longitudinal movement of air produces pressure fluctuations.

answer is D.

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Detailed Solution

We say the compressions and refractions in a sound wave exist because sound can reflect off fixed ends and interfere with incident waves, and vibrates longitudinally. This longitudinal movement of air produces pressure fluctuations.
A sound wave is a longitudinal wave, i.e., the vibration of the particles of the medium through which it propagates is back and forth. For example, consider a sound wave that propagates from left to right through the air. Here, the propagation medium is air, and the air particles will get displaced to the left and the right as sound travels. This longitudinal motion of the particles results in compressions and refractions since, in some regions, the air particles are compressed together, and in other regions, the air particles spread out. These compressed regions and spread-out regions constitute high-pressure regions and low-pressure regions. The compression and expansion of air create a difference in air pressure. Thus a sound wave is often referred to as a pressure wave. Like the human ear, a detector detects pressure changes when it hears a sound. It might immediately notice a pressure that indicates compression. The following instant, it notices a normal pressure followed by a low pressure consistent with a rarefaction.

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