Decibel Questions

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Very Short Answers Questions [1 Mark Questions]

Ques. One decibel is one-tenth of _______

1. 10 bel
2. 100 bel
3. 1 bel
4. 1000 bel

Ans. The correct answer is c. 1 bel

Explanation: The decibel (dB) is a unit of measurement that equals one-tenth of a bel (B).

Ques. Decibel is named after ______

1. Albert Einstein
2. Michael Faraday
3. Newton
4. Alexander Graham Bell

Ans. The correct answer is d. Alexander Graham Bell

Explanation: Decibel is named after the scientist Alexander Graham Bell.

Ques. ______ provides a relative measure of sound intensity.

1. Decibels
2. Luminous intensity
3. Radians
4. Watts

Ans. The correct answer is a. Decibels

Explanation: Decibels are a measure of the relative intensity of sound.

Ques. Elephants use _____ sounds to interact with herds hundreds of kilometers away.

1. Supersonic
2. Infrasonic
3. Ultrasonic
4. Sonic

Ans. The correct answer is b. Infrasonic

Explanation: Elephants communicate with herds hundreds of kilometers away using infrasonics.

Ques. Which instrument is used to study noise pollution to analyze the quantification of various kinds of noise?

1. Speedometer
2. Accelerometer
3. Microphones
4. Sound level meters

Ans. The correct answer is d. Sound level meters

Explanation: Sound level meters are used for measuring the intensity of sound in decibels.

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Short Answers Questions [2 Marks Questions]

Ques. Define the decibel scale.

Ans. The decibel is the unit of measurement for sound. It is denoted by 'dB'. Decibel is a unit of measurement used to describe the ratio of one value of a power or field quantity to another on a logarithmic scale, where the logarithmic quantity is referred to as the power level or field level.

Ques. What is a Decibel Meter?

Ans. Decibel meters measure sound pressure in order to determine noise levels. A sound level meter, also known as a sound pressure level (SPL) meter, decibel (dB) meter, noise meter, or noise dosimeter, captures sound using a microphone. The instrument then evaluates the sound and displays acoustic measurement data.

Ques. What do you mean by Sound?

Ans. Sounds are vibrations that are created by any source. Ideally, it flows across media such as water or air. It can be shown that sound waves are acoustic and may spread through land or earth.

Ques. What is meant by the sonic boom?

Ans. A sonic boom is a sound related to shock waves produced when an object moves faster than the speed of sound through the air. Sonic booms produce massive volumes of sound energy, like an explosion or a thunderclap to the human ear.

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Long Answers Questions [3 Marks Questions]

Ques. What are the applications of decibels?

Ans. The deciBel, abbreviated dB, is commonly used in a variety of applications.

• It is used in many different types of measurements in engineering and science, notably in electronics, acoustics, and control theory.
• The decibel, dB, is commonly used to define amplifier gains, component losses (e.g., attenuators, feeders, mixers, etc.), and a variety of other metrics such as noise figure, signal-to-noise ratio, and many more.
• Because of its logarithmic scale, the deciBel can easily express very large ratios in terms of reasonable integers while still allowing for ratio multiplication by simple addition and subtraction.
• The deciBel is a popular unit of measurement for sound intensity or sound pressure level. For this, the sound is referenced to a pressure of 0.0002 microbars, which corresponds to the standard for hearing threshold.

Ques. What is the difference between Decibel and Hertz?

Ans. The following are the differences between Decibel and Hertz

Ques. Why should an employer maintain a sound level in the workplace?

Ans. Maintaining a sound level or lowering decibels improves the working environment for employees. 

• This is also an excellent method of protecting an employee's mental health. 
• It is a well-known fact that noise increases workplace stress. 
• High-pitched noise disrupts normal conversation and causes distraction in the workplace. 
• As a result, regulating sound levels is essential in the workplace.

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Very Long Answers Questions [5 Marks Questions]

Ques. In a test of a subsonic jet, the jet flies overhead at an altitude of 100 m. The sound intensity on the ground as the Jet passes overhead is 160 dB. At what altitude should the jet plane fly so that the ground noise is not greater than 120 dB?

Ans. Let L be the initial loudness of the sound wave. Then the initial intensity (I) of the sound is given by

L = 10 log₁₀ (I/I₀)

Where I₀ is the threshold of hearing.

But, I = I₀/r²

Where r is the distance from the sound source

⇒ L = 10 log₁₀ (1/r²)

Given, for r = 100 m, L = 160 dB

On substituting the values, we get

160 = 10 log₁₀ (1/100²) …(i)

Now let x be the altitude of the jet at which the loudness is 120 dB. Therefore using

L = 10 log₁₀ (1/r²)

⇒ 120 = 10 log₁₀ (1/x²) …(ii)

Subtracting equation (ii) from (i), we get

160 - 120 = 10 log₁₀ (1/100²) - 10 log₁₀ (1/x²)

⇒ 40 = 10 [log₁₀ (1/100²) - log₁₀ (1/x²)]

⇒ 4 = [log₁₀ (1/100²) - log₁₀ (1/x²)]

⇒ 4 = log₁₀ x²/10000

⇒ x = 10000 m = 10 km

Hence, the jet should fly at an altitude of above 10 km such that the ground noise is not greater than 120 dB.

Ques. By what factor must the sound intensity be increased to increase the sound intensity level by 13.0 dB?

Ans. Let L be the initial loudness of the sound. Then the initial intensity (I) of the sound is given by

L = 10 log₁₀ (I/I₀)

Where I₀ is the threshold of hearing.

Let, when loudness is increased by 13 dB, the intensity becomes nI. Therefore

L + 13 = 10 log₁₀ (nI/I₀)

⇒ L + 13 = 10 [log₁₀ n + log₁₀ (I/I₀)]

⇒ L + 13 = 10 log₁₀ n + 10 log₁₀ (I/I₀)

But 10 log₁₀ (I/I₀) = L, therefore

L + 13 = 10 log₁₀ n + L

⇒ log₁₀ n = 13/10

⇒ log₁₀ n = 1.3

⇒ n = 101.3 ≅ 20

Ques. The loudness of a source of sound at a given location increases by 20 dB. By how many times does its intensity increase?

Ans. Then the initial intensity (I) of the sound is given by

L = 10 log₁₀ (I/I₀)

Where I₀ is the threshold of hearing.

Let, when loudness is increased by 20 dB, the intensity becomes nI. Therefore

L + 20 = 10 log₁₀ (nI/I₀)

⇒ L + 20 = 10 [log₁₀ n + log₁₀ (I/I₀)]

⇒ L + 20 = 10 log₁₀ n + 10 log₁₀ (I/I₀)

But 10 log₁₀ (I/I₀) = L, therefore

L + 20 = 10 log₁₀ n + L

⇒ log₁₀ n = 20/10

⇒ log₁₀ n = 2

⇒ n = 10² = 100

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