Which of the following pairs is correctly matched? 1. Infrasound : Frequency 20 kHz 3. Audible Range : 20 Hz – 2000 Hz Select the correct answer using the code given below:

The correct option is 1 and 2 only Explanation Sound waves are longitudinal mechanical waves classified based on their frequency relative to the human hearing capacity. The acoustic spectrum is divided into three main categories: infrasonic, audible, and ultrasonic waves. Statement-wise Analysis: - Statement 1 is Correct: Infrasound refers to sound waves with frequencies below the lower limit of human audibility, which is 20 Hz. These waves are produced by sources such as earthquakes, volcanoes, and certain animals like whales and elephants. - Statement 2 is Correct: Ultrasound refers to sound waves with frequencies exceeding the upper limit of human audibility, which is 20,000 Hz (20 kHz). These waves are utilized in applications such as SONAR and medical ultrasonography. - Statement 3 is Incorrect: The Audible Range for the average human ear extends from 20 Hz to 20,000 Hz (20 kHz). The statement incorrectly cites the upper limit as 2000 Hz. Frequencies above 20 kHz are inaudible to humans. Key Takeaway: The classification of sound by frequency is: Infrasound ( 20 kHz).

NCERT Class 9 Science — Chapter 5: Sound

mcqeasy

Which of the following pairs is correctly matched?

Infrasound : Frequency < 20 Hz
Ultrasound : Frequency > 20 kHz
Audible Range : 20 Hz – 2000 Hz

Select the correct answer using the code given below:

Official previous-year question

Verified 1 Aug 2026.

Options

A1, 2 and 3
B2 and 3 only
C1 and 2 only
D1 and 3 only

Did you get this right?

Solution

The correct option is

1 and 2 only

Explanation

Sound waves are longitudinal mechanical waves classified based on their frequency relative to the human hearing capacity. The acoustic spectrum is divided into three main categories: infrasonic, audible, and ultrasonic waves.

Statement-wise Analysis:

Statement 1 is Correct: Infrasound refers to sound waves with frequencies below the lower limit of human audibility, which is 20 Hz. These waves are produced by sources such as earthquakes, volcanoes, and certain animals like whales and elephants.
Statement 2 is Correct: Ultrasound refers to sound waves with frequencies exceeding the upper limit of human audibility, which is 20,000 Hz (20 kHz). These waves are utilized in applications such as SONAR and medical ultrasonography.
Statement 3 is Incorrect: The Audible Range for the average human ear extends from 20 Hz to 20,000 Hz (20 kHz). The statement incorrectly cites the upper limit as 2000 Hz. Frequencies above 20 kHz are inaudible to humans.

Key Takeaway:
The classification of sound by frequency is: Infrasound (< 20 Hz), Audible Sound (20 Hz – 20 kHz), and Ultrasound (> 20 kHz).

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

1 and 2 only

Explanation

Statement-wise Analysis:

Statement 1 is Correct: Infrasound refers to sound waves with frequencies below the lower limit of human audibility, which is 20 Hz. These waves are produced by sources such as earthquakes, volcanoes, and certain animals like whales and elephants.
Statement 2 is Correct: Ultrasound refers to sound waves with frequencies exceeding the upper limit of human audibility, which is 20,000 Hz (20 kHz). These waves are utilized in applications such as SONAR and medical ultrasonography.
Statement 3 is Incorrect: The Audible Range for the average human ear extends from 20 Hz to 20,000 Hz (20 kHz). The statement incorrectly cites the upper limit as 2000 Hz. Frequencies above 20 kHz are inaudible to humans.

Key Takeaway:
The classification of sound by frequency is: Infrasound (< 20 Hz), Audible Sound (20 Hz – 20 kHz), and Ultrasound (> 20 kHz).