Acoustics Questions

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Very Short Answers Questions [1 Mark Questions]

Ques. What is acoustics?

Ans. Acoustics is a science that studies sound generation, control, transmission, reaction, and other sound qualities.

Ques. The intensity of sound is proportion to___________of amplitude.

1. Square root
2. Square
3. Cube root
4. Cube

Ans. The correct answer is c. Cube root

Explanation: The quantity of wave energy traveling across a unit area per unit of time is defined as intensity. The area where it is taken is perpendicular to the direction of the propagation of the wave. Sound intensity is proportional to the square of the amplitude.

Ques. Which law states that the magnitude of a sensation is directly proportional to the logarithm of the physical stimulus producing it?

1. Huygens-Fresnel Law
2. Beer-Lambert Law
3. Weber and Fechner's Law
4. Lorentz Law

Ans. The correct answer is c. Weber and Fechner's

Explanation: According to Weber and Fechner's law, the amplitude of a sensation is precisely proportional to the logarithm of the physical stimulus that causes it. For example, loudness, which represents the amplitude of the sensation, is proportional to the logarithm of the sound's intensity.

Ques. What is psychoacoustics?

Ans. Psychophysics is a field of physics that studies sound perception and audiology scientifically.

Ques. The intensity of sound depends on the ear of the listener,

1. True
2. False

Ans. The correct answer is b. False

Explanation: The intensity of sound is independent of the listener's ear. However, loudness does not depend on the listener's ear. There is a chance that the same listener may make different decisions regarding the loudness of sounds with the same intensity but different frequencies.

Ques. Which of the following statements is correct?

1. The pitch of the sound decreases with an increase in frequency
2. The pitch of the sound decreases with an increase in frequency
3. An increase in the amplitude of the sound decreases the intensity
4. Decibel is equal to 1/100 of bel

Ans. The correct answer is b. The pitch of the sound decreases with an increase in frequency

Explanation: The pitch of the sound increases as the frequency increases. A decibel is one-tenth of a bel. The intensity of a sound increases as its amplitude increases.

Ques. Which of the following is not a characteristic of sound?

1. Frequency
2. Intensity
3. Quality
4. Speed

Ans. The correct answer is d. Speed

Explanation: There are three characteristics of sound. These are frequency and pitch, intensity and loudness, and quality or timbre.

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Short Answers Questions [2 Marks Questions]

Ques. What are the types of acoustics?

Ans. The following are the types of acoustics

• Environmental Noise
• Vibration and Dynamics
• Infrasound
• Ultrasounds
• Musical Acoustics

Ques. Why are the ceilings of concert halls curved? Explain.

Ans. The concert hall's ceilings are curved to reflect sound from the ceiling to every corner of the concert hall, allowing the audience to hear sound quite well.

Ques. As compared to a dry day, why does sound travel faster on a rainy day?

Ans. During rainy days, the atmosphere becomes more humid. The speed of sound typically rises with humidity, and the speed of sound in water is four times that of sound in air. As a result, on a rainy day, sound travels quicker.

Ques. Name the stages of an acoustic event.

Ans. The following phases are included in an acoustic event:

1. Mechanism of generation or cause
2. The impact of reception
3. Propagation of acoustic waves

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Long Answers Questions [3 Marks Questions]

Ques. What will be the frequency of sound having 0.20 m as its wavelength, when it travels with a speed of 331 ms^-1?

Ans. Given

• The wavelength of the sound, λ = 0.20 m
• The speed of sound, v = 331 ms^-1

The frequency of sound, f = v/λ

⇒ f = 331/0.20 = 1655 Hz

Ques. What is Sonar?

Ans. Sound Navigation and Ranging (SONAR) uses an echo-surrounding method to detect targets using ultrasound. It is an acoustic technology in which a high-frequency sound pulse is sent and then received after being reflected by objects such as submarines.

Ques. List some medical applications of Ultrasonic in industries.

Ans. Some medical applications of Ultrasonic are

• Ultrasonic waves are utilized in diagnostics to identify malignancies.
• Ultrasonic waves are used extensively in the treatment of disorders such as neuralgia pain.
• Ultrasonic waves can also be used in surgery to remove brain tumors and kidney stones without causing blood loss.

Ques. Why does an empty container produce more sound than a filled one?

Ans. An empty container contains nothing but air. As a result, anytime sound is produced in an empty container, vibrations increase due to multiple reflections in the air molecule. However, because there are so few air molecules in a packed container, it does not make any more sound.

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Very Long Answers Questions [5 Marks Questions]

Ques. What is the loudness of sound? What factors does it depend on?

Ans. Loudness is a sound quality that causes the ear to respond to the sound. It is the energy contained in a sound wave. Sound pressure is another term for the loudness of a sound. It essentially measures the intensity of sound.

• Decibels (dB) are used to measure loudness. 
• The decibel scale compares the strength of a pressure wave to that of a normal pressure wave. 
• The sound waves are quite intense at high decibel levels. 
• As a result, the volume or loudness of the sound is increased. 
• The amplitude of the wave determines the loudness of a sound.
• The loudness of sound is proportional to the square of the amplitude. 
• The sensitivity of the human ear also influences the loudness of sound.

Ques. The intensity of the sound of a jet flying at an altitude of 150 m is observed to be 140 dB. What is the height of the jet such that its intensity drops to 120 dB?

Ans. Given, for height, r¹ = 150 m, the loudness, L₁ = 140 dB

Let at height r² = x, the loudness will be, L₂ = 120 dB

As each 10 dB rise in loudness, the intensity will increase by 10 times. Hence, for each 10 dB fall in loudness, the intensity will decrease by (1/10)th times.

Decrease in the loudness = L₁ - L₂ = 140 - 120 = 20 dB = (2 x 10) dB

Therefore, the drop in the intensity will be (1/10 x 1/10 = 1/10² times) the initial value.

Now let the initial intensity be I, then the final intensity will be (I/10²).

The intensity of sound is inversely proportional to the square of the distance from the source. i.e. I ∝ 1/r²

∴ I₁ / I₂ = (1/r₁²) / (1/r₂²)

Given

• The initial intensity of the sound, I₁ = I
• The final intensity of the sound, I₂ = I/10²
• Initial altitude, r¹ = 150 m

∴ I / (I/10²) = (1/150)² / (1/x)²

⇒ 10² = (x²/150²)

⇒ x² = 150² x 10²

⇒ x² = 225 x 10² x 10² = 225 x 10⁴

⇒ x = 1500 m

Ques. An ultrasonic wave is sent from a ship toward the bottom of the sea. It is found that the time interval between the transmission and reception of the wave is 1.6 seconds. What is the depth of the sea, if the velocity of sound in the seawater is 1400 ms^-1?

Ans. Given

• The time interval between sending and receiving of the wave, t = 1.6 s
• The velocity of sound in sea wave, v = 1400 ms^-1

Since the time taken by the wave to go to the depth and then return to the ship is 1.6 s, therefore the wave takes half of the time to reach the depth i.e. 1.6/2 = 0.8 s

Using the formula

Speed = Distance / Time

⇒ Distance = Speed x Time

Solution

2d = V x t

depth of the sea, d = [ 1400 x 1.6 ] / 2

= 2240 /2

= 1120 m

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