NCERT Class 9 Science — Chapter 5: Sound

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Which of the following phenomena is primarily responsible for the 'rolling' effect of thunder?

Official previous-year question

Verified 1 Aug 2026.

Options

AThe high energy of the lightning bolt.
BThe variation in speed of sound due to temperature changes.
CThe interference of sound waves from different clouds.
DThe successive reflections of sound from clouds and land.

Did you get this right?

Solution

The correct option is

The successive reflections of sound from clouds and land.

Explanation

Thunder is the acoustic shockwave produced by the rapid heating and expansion of air surrounding a lightning bolt. While the visual flash is instantaneous, the associated sound is often heard as a prolonged rumble or "roll" rather than a single sharp crack.

Detailed Analysis:

The high energy of the lightning bolt. is incorrect: The high energy of the lightning bolt is responsible for the initial generation of the shockwave (the loud crack), but it does not account for the prolonged duration or the rolling characteristic of the sound.
The successive reflections of sound from clouds and land. is correct: The rolling effect is primarily caused by successive reflections (reverberation) of sound waves. The sound generated by the lightning reflects off various surfaces, such as clouds, the ground, hills, and buildings. Because these reflected waves travel different path lengths, they arrive at the listener's ear at different times, creating a continuous, rumbling effect. Additionally, since a lightning bolt can be several kilometers long, sound from the farther end of the bolt takes longer to reach the observer than sound from the nearer end, further contributing to the duration.
The interference of sound waves from different clouds. is incorrect: Interference involves the superposition of waves leading to regions of maximum and minimum intensity (beats). While this may cause fluctuations in loudness, it is not the primary cause of the prolonged rolling effect.
The variation in speed of sound due to temperature changes. is incorrect: Variations in temperature cause the refraction of sound waves, which affects the distance thunder can travel and the direction it bends. While this influences audibility, it is not the main cause of the rolling phenomenon.

Key Takeaway: The rolling of thunder is primarily due to the multiple reflections of sound from clouds and land surfaces, as well as the time difference in sound arrival from different parts of the long lightning bolt.

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?

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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?

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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:

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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?

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The correct option is

The successive reflections of sound from clouds and land.

Explanation

Detailed Analysis:

The high energy of the lightning bolt. is incorrect: The high energy of the lightning bolt is responsible for the initial generation of the shockwave (the loud crack), but it does not account for the prolonged duration or the rolling characteristic of the sound.
The successive reflections of sound from clouds and land. is correct: The rolling effect is primarily caused by successive reflections (reverberation) of sound waves. The sound generated by the lightning reflects off various surfaces, such as clouds, the ground, hills, and buildings. Because these reflected waves travel different path lengths, they arrive at the listener's ear at different times, creating a continuous, rumbling effect. Additionally, since a lightning bolt can be several kilometers long, sound from the farther end of the bolt takes longer to reach the observer than sound from the nearer end, further contributing to the duration.
The interference of sound waves from different clouds. is incorrect: Interference involves the superposition of waves leading to regions of maximum and minimum intensity (beats). While this may cause fluctuations in loudness, it is not the primary cause of the prolonged rolling effect.
The variation in speed of sound due to temperature changes. is incorrect: Variations in temperature cause the refraction of sound waves, which affects the distance thunder can travel and the direction it bends. While this influences audibility, it is not the main cause of the rolling phenomenon.