NCERT Class 9 Science — Chapter 5: Sound

mcqeasy

Which of the following correctly describes the relationship between the density of a medium and the pressure in a sound wave?

Official previous-year question

Verified 1 Aug 2026.

Options

AHigher density corresponds to higher pressure.
BPressure remains constant while density varies.
CHigher density corresponds to lower pressure.
DDensity and pressure are unrelated in a sound wave.

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Solution

The correct option is

Higher density corresponds to higher pressure.

Explanation

Sound propagates through a medium as a longitudinal mechanical wave. This propagation involves the oscillation of medium particles parallel to the direction of wave motion, creating alternating regions known as compressions and rarefactions.

Analysis of Density and Pressure Relationship:

Compressions: These are regions where the particles of the medium are pushed close together. This crowding results in high density. Due to the increased concentration of particles, the pressure in this region also increases. Thus, compressions represent zones of high density and high pressure.
Rarefactions: These are regions where the particles of the medium are spread farther apart. This dispersion results in low density. Consequently, the pressure in this region decreases. Thus, rarefactions represent zones of low density and low pressure.
Conclusion: Density and pressure in a sound wave are directly correlated and oscillate in phase. A point of maximum density coincides with a point of maximum pressure.

Key Takeaway: In a sound wave, variations in density and pressure occur simultaneously; higher density always corresponds to higher pressure (compression), and lower density corresponds to lower pressure (rarefaction).

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?

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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

Higher density corresponds to higher pressure.

Explanation

Analysis of Density and Pressure Relationship:

Compressions: These are regions where the particles of the medium are pushed close together. This crowding results in high density. Due to the increased concentration of particles, the pressure in this region also increases. Thus, compressions represent zones of high density and high pressure.
Rarefactions: These are regions where the particles of the medium are spread farther apart. This dispersion results in low density. Consequently, the pressure in this region decreases. Thus, rarefactions represent zones of low density and low pressure.
Conclusion: Density and pressure in a sound wave are directly correlated and oscillate in phase. A point of maximum density coincides with a point of maximum pressure.