NCERT Class 9 Science — Chapter 5: Sound

mcqeasy

In the context of sound waves, what does the term 'Compression' represent?

Official previous-year question

Verified 1 Aug 2026.

Options

AA region where particles are crowded together.
BA region of low pressure.
CA region where the density of the medium is minimum.
DA region where particles are spread apart.

Did you get this right?

Solution

The correct option is

A region where particles are crowded together.

Explanation

Sound waves propagate through a medium as longitudinal mechanical waves. This propagation occurs through the oscillation of particles back and forth parallel to the direction of energy transport, creating alternating regions of varying density and pressure known as compressions and rarefactions.

Detailed Analysis

Compression: This represents a region in a longitudinal wave where the particles of the medium are crowded together. Consequently, this is a zone of high density and high pressure.
Rarefaction: This represents a region where the particles are spread apart. This results in a zone of low density and low pressure.

Analyzing the options based on these definitions:

A region where particles are spread apart.: Describes a rarefaction (particles spread apart).
A region of low pressure.: Describes a rarefaction (low pressure).
A region where particles are crowded together.: Correctly describes a compression (particles crowded together).
A region where the density of the medium is minimum.: Describes a rarefaction (minimum density).

Key Takeaway: In a longitudinal sound wave, Compression is characterized by maximum density and pressure, while Rarefaction is characterized by minimum density and pressure.

Your note

More from Chapter 5: Sound

Consider the following statements regarding the propagation of sound: 1. The disturbance created by a source travels through the medium to the listener. 2. Sound waves are characterized as non-mechanical waves. 3. A material medium is mandatory for the transmission of sound. Which of the statements given above are correct?

medium

With reference to the characteristics of a sound wave, consider the following statements: 1. The distance between two consecutive compressions is called the wavelength. 2. The time taken for one complete oscillation is called the frequency. 3. The SI unit of frequency is Hertz. Which of the statements given above are correct?

medium

Consider the following statements regarding Ultrasound: 1. It refers to sounds with frequencies higher than 20 kHz. 2. Ultrasound waves scatter immediately when they encounter obstacles. 3. Ultrasound is incapable of penetrating metal blocks to detect flaws. Which of the statements given above is/are correct?

easy

The cleaning action of an ultrasonic cleaner is primarily achieved through:

medium

With reference to medical applications of sound, consider the following statements: 1. Echocardiography uses ultrasonic waves to form an image of the heart. 2. Ultrasonography uses X-rays to detect stones in the gall bladder. 3. Ultrasound can be used to break kidney stones into fine grains. Which of the statements given above are correct?

medium

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The correct option is

A region where particles are crowded together.

Explanation

Detailed Analysis

Compression: This represents a region in a longitudinal wave where the particles of the medium are crowded together. Consequently, this is a zone of high density and high pressure.
Rarefaction: This represents a region where the particles are spread apart. This results in a zone of low density and low pressure.

Analyzing the options based on these definitions:

A region where particles are spread apart.: Describes a rarefaction (particles spread apart).
A region of low pressure.: Describes a rarefaction (low pressure).
A region where particles are crowded together.: Correctly describes a compression (particles crowded together).
A region where the density of the medium is minimum.: Describes a rarefaction (minimum density).

Key Takeaway: In a longitudinal sound wave, Compression is characterized by maximum density and pressure, while Rarefaction is characterized by minimum density and pressure.