Question

The unit used to measure sound intensity level is:

• A. Hertz
• B. Decibel
• C. Pascal
• D. Joule

Hint:

Always remember: {Sound intensity level = Decibel (dB)} and {Frequency = Hertz (Hz)}.

Answer 1

The Correct Option is B

The question asks about the unit used to measure sound intensity level. Let's examine the options provided:

1. Hertz: This is a unit of frequency, which measures the number of cycles per second of a periodic phenomenon. It is not used to measure sound intensity level.
2. Decibel: This is the correct option. The decibel (dB) is a logarithmic unit used to measure the intensity of sound. It quantifies sound levels relative to a reference level, typically the threshold of hearing, which is defined as 0 dB.
3. Pascal: This unit is used to measure pressure. While sound waves do create pressure variations, the pascal is not used to measure the sound intensity level directly.
4. Joule: This unit measures energy or work. It is not related to measuring sound intensity level.

Therefore, the correct answer is Decibel. This is because the sound intensity level indicates how much sound power passes through a certain area, and the decibel scale provides a convenient way to express these levels in a manageable range, using a logarithmic scale.

To elaborate, sound intensity level in decibels (dB) is calculated using the formula:

\(L = 10 \log_{10} \left(\frac{I}{I_0}\right)\)

where:

• \( L \) is the sound intensity level in decibels.
• \( I \) is the intensity of the sound wave.
• \( I_0 \) is the reference intensity, usually \( 10^{-12} \, \text{W/m}^2 \), which is the threshold of human hearing.

This logarithmic scale means that an increase of 10 dB represents a tenfold increase in intensity, which makes it easier to represent the wide range of hearing in human experiences.

Answer 2

Step 1: Understanding sound intensity and sound intensity level. 
Sound intensity is defined as the sound power transmitted per unit area perpendicular to the direction of sound propagation. However, the human ear cannot perceive sound intensity on a linear scale; instead, it responds logarithmically to changes in sound intensity. Therefore, sound intensity is expressed in terms of sound intensity level. 
Step 2: Definition of sound intensity level. 
Sound intensity level is a logarithmic measure of sound intensity relative to a reference intensity. It is given by the formula: \[ L = 10 \log_{10} \left( \frac{I}{I_0} \right) \] where \( I \) is the sound intensity and \( I_0 \) is the reference sound intensity. The unit of sound intensity level is the decibel (dB). 
Step 3: Reason for using decibel scale. 
The decibel scale compresses a very wide range of sound intensities into a manageable scale. This makes it suitable for representing noise levels in environmental studies and noise pollution assessment. 
Step 4: Analysis of options. 
(A) Hertz: Hertz is the unit of frequency and measures the pitch of sound, not intensity level. 
(B) Decibel: Correct — Decibel is the standard unit used to measure sound intensity level on a logarithmic scale. 
(C) Pascal: Pascal is the unit of pressure and is used to measure sound pressure, not sound intensity level. 
(D) Joule: Joule is the unit of energy and has no direct relation to sound intensity level. 
Step 5: Final conclusion. 
Since sound intensity level is expressed on a logarithmic scale and measured in decibels, the correct answer is (B) Decibel.