Which of the following statements is INCORRECT? | Technical Ability MCQ | Examoogle

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Which of the following statements is INCORRECT?

Option 1

Option 2

Option 3

Option 4

Correct Answer

⚙️ TE • Technical Concept & PrincipleTechnical AbilityCivil Engineering

Option A

Option 1

Quick Summary:

The statement claiming that the threshold of human hearing is approximately $10$ micropascals is incorrect. The standard reference sound pressure for hearing in air is actually $20$ micropascals ( $\mu Pa$ ), which corresponds to $0$ dBSPL (Sound Pressure Level).

⚙️TETechnical SolutionConcept & Principle

📜 Standard Reference & Code Clause

ISO 1683:2015 (Acoustics - Preferred reference quantities for acoustic levels)

💡 Explanation

🔢 Key Formulas

$L_p = 20 \log_{10} \left( \frac{p}{p_0} \right) \text{ dB}$ — Sound Pressure Level formula where $p_0 = 20 \mu\text{Pa}$

$L_I = 10 \log_{10} \left( \frac{I}{I_0} \right) \text{ dB}$ — Sound Intensity Level formula where $I_0 = 10^{-12} \text{ W/m}^2$

⚙️ Working Principle

Sound levels are measured on a logarithmic scale because human perception of sound intensity is non-linear and spans a massive range. A reference value ( $Q_0$ or $p_0$ ) is essential to define the baseline of $0$ dB, which is set to the absolute threshold of hearing for a healthy human ear at $1$ kHz.

📌 Key Points

▸
The threshold of human hearing in air is $20 \mu\text{Pa}$ ( $2 \times 10^{-5} \text{ Pa}$ ).
▸
Sound pressure levels are calculated using a logarithmic scale to compress the vast range of human auditory sensitivity.
▸
Bels are the base unit of the logarithmic ratio, but decibels (dB) are commonly used as the practical unit.
▸
Sound intensity ( $I$ ) is proportional to the square of sound pressure ( $p$ ), hence the factor of $20$ in the pressure formula versus $10$ in the intensity formula.

✅ Advantages

▸
Logarithmic scales simplify calculations involving ratios.
▸
Matches the human ear's logarithmic response to stimulus.

❌ Disadvantages / Limitations

▸
Requires reference points to be meaningful.
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Can be confusing due to different reference values for different media (e.g., $1 \mu\text{Pa}$ for underwater sound).

🛠️ Applications / Uses

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Environmental noise monitoring.
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Acoustic engineering and room design.
▸
Audio equipment specification.

📄 Additional Information

▸
The reference sound pressure in air is fixed at $20 \mu\text{Pa}$ for international standardization.
▸
Option D is incorrect because it cites $10 \mu\text{Pa}$ , which is half the actual standardized threshold.

📊 Diagram / Illustration

✅

D is correct — The value $10 \mu\text{Pa}$ is scientifically inaccurate as the threshold of human hearing is standardized at $20 \mu\text{Pa}$ .

Core Concepts Used

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Acoustics Logarithmic Sound Scales Threshold of Hearing

💡 EXAM TIP

Always remember the standard reference pressure for air is $20 \mu\text{Pa}$ and for water is $1 \mu\text{Pa}$ , as exam questions often swap these to test conceptual clarity.

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