Consider the following statements regarding the 'Amplitude' of a sound wave: 1. It is represented by the letter Z. 2. Its unit is the same as that of density or pressure. 3. It depends upon the force with which an object is made to vibrate. Which of the statements given above are correct?

The correct option is (c). Explanation Sound waves are longitudinal waves characterized by the propagation of compressions and rarefactions in a medium. These waves are defined by variables such as frequency, amplitude, and speed. Amplitude refers to the magnitude of the maximum disturbance in the medium on either side of the mean value. Statement-wise Analysis: - Statement 1 is Incorrect: The amplitude of a sound wave is conventionally represented by the letter A. The letter Z is typically used to denote acoustic impedance or atomic number in other contexts. - Statement 2 is Correct: Since sound waves propagate as variations in the medium's density and pressure, the disturbance can be measured in terms of these physical quantities. Therefore, the unit of amplitude corresponds to the unit of the quantity being measured, which is either density (kg/m³) or pressure (Pascal). - Statement 3 is Correct: The amplitude corresponds to the energy of the wave. It depends directly on the force with which the source object is made to vibrate. A stronger force causes a larger displacement from the equilibrium position, resulting in a higher amplitude and a louder sound. Key Takeaway: Amplitude determines the loudness of a sound. It represents the maximum variation in density or pressure from the equilibrium state and is directly proportional to the force applied to generate the vibration.

NCERT Class 9 Science — Chapter 5: Sound

mcqmedium

Consider the following statements regarding the 'Amplitude' of a sound wave:

It is represented by the letter Z.
Its unit is the same as that of density or pressure.
It depends upon the force with which an object is made to vibrate.

Which of the statements given above are correct?

Official previous-year question

Verified 1 Aug 2026.

Options

A1 and 2 only
B2 only
C2 and 3 only
D1, 2 and 3

Did you get this right?

Solution

The correct option is (c).

Explanation

Sound waves are longitudinal waves characterized by the propagation of compressions and rarefactions in a medium. These waves are defined by variables such as frequency, amplitude, and speed. Amplitude refers to the magnitude of the maximum disturbance in the medium on either side of the mean value.

Statement-wise Analysis:

Statement 1 is Incorrect: The amplitude of a sound wave is conventionally represented by the letter A. The letter Z is typically used to denote acoustic impedance or atomic number in other contexts.
Statement 2 is Correct: Since sound waves propagate as variations in the medium's density and pressure, the disturbance can be measured in terms of these physical quantities. Therefore, the unit of amplitude corresponds to the unit of the quantity being measured, which is either density (kg/m³) or pressure (Pascal).
Statement 3 is Correct: The amplitude corresponds to the energy of the wave. It depends directly on the force with which the source object is made to vibrate. A stronger force causes a larger displacement from the equilibrium position, resulting in a higher amplitude and a louder sound.

Key Takeaway:
Amplitude determines the loudness of a sound. It represents the maximum variation in density or pressure from the equilibrium state and is directly proportional to the force applied to generate the vibration.

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

Keep practising Chapter 5: Sound

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The correct option is (c).

Explanation

Statement-wise Analysis:

Statement 1 is Incorrect: The amplitude of a sound wave is conventionally represented by the letter A. The letter Z is typically used to denote acoustic impedance or atomic number in other contexts.
Statement 2 is Correct: Since sound waves propagate as variations in the medium's density and pressure, the disturbance can be measured in terms of these physical quantities. Therefore, the unit of amplitude corresponds to the unit of the quantity being measured, which is either density (kg/m³) or pressure (Pascal).
Statement 3 is Correct: The amplitude corresponds to the energy of the wave. It depends directly on the force with which the source object is made to vibrate. A stronger force causes a larger displacement from the equilibrium position, resulting in a higher amplitude and a louder sound.