Rarefaction

Definition

Rarefaction is a region in a wave where the medium is less dense compared to the surrounding areas. It is a key concept in understanding the propagation of sound waves and their behavior, particularly in the context of the speed of sound, frequency, wavelength, the Doppler effect, and sonic booms.

5 Must Know Facts For Your Next Test

1. Rarefaction is a key characteristic of longitudinal waves, such as sound waves, where the medium (e.g., air) expands and becomes less dense compared to the surrounding areas.
2. The speed of sound is influenced by the properties of the medium, including its density, which is affected by rarefaction and compression regions in the wave.
3. The frequency and wavelength of a sound wave are inversely related, and the relationship is affected by the speed of sound, which is influenced by rarefaction.
4. The Doppler effect, which describes the change in observed frequency of a wave due to the relative motion between the source and the observer, is directly related to the compression and rarefaction regions of the wave.
5. Sonic booms are caused by the compression and rarefaction regions of a supersonic object, creating a shock wave that can be heard as a loud, sudden noise.

Review Questions

• Explain how rarefaction affects the speed of sound in a medium.
  • Rarefaction, as a region of lower density in a medium, impacts the speed of sound propagation. The speed of sound is directly related to the properties of the medium, including its density. In a region of rarefaction, where the medium (e.g., air) is less dense, the speed of sound will be lower compared to the surrounding areas of higher density. This is because the molecules in the rarefied region have less interaction and collisions, which are necessary for the efficient transmission of the sound wave.
• Describe the relationship between rarefaction, frequency, and wavelength of a sound wave.
  • The frequency and wavelength of a sound wave are inversely related, and this relationship is influenced by the speed of sound, which is affected by rarefaction. As the medium experiences rarefaction, the speed of sound decreases. Since the speed of sound is equal to the product of the frequency and wavelength, a decrease in the speed of sound will result in a corresponding decrease in the frequency and an increase in the wavelength of the sound wave, or vice versa. This interplay between rarefaction, speed of sound, frequency, and wavelength is crucial in understanding the propagation of sound waves.
• Analyze the role of rarefaction in the formation of sonic booms and the Doppler effect.
  • Rarefaction plays a crucial role in the formation of sonic booms and the Doppler effect. When an object moves at a speed greater than the speed of sound, it creates a shock wave with regions of compression and rarefaction. The sudden changes in the medium's density, caused by these compression and rarefaction regions, result in the characteristic loud, sudden noise known as a sonic boom. Additionally, the Doppler effect, which describes the change in observed frequency of a wave due to the relative motion between the source and the observer, is directly related to the compression and rarefaction regions of the wave. As the source moves, the compression and rarefaction regions shift, leading to the observed change in frequency, which is a key indicator of the Doppler effect.

Related terms

Compression:

A region in a wave where the medium is more dense compared to the surrounding areas, opposite of rarefaction.

Longitudinal Wave: A wave in which the displacement of the medium is parallel to the direction of wave propagation, such as sound waves.

Interference:

The interaction of two or more waves, resulting in a new wave pattern due to the superposition of the individual wave displacements.