Which one of the following statements is not correct?
The sensitivity of the human ear does not vary with the frequency of the sound.
Understanding Sound and Hearing: Identifying the Incorrect Statement
The question asks us to identify the statement that is not correct among the given options related to sound waves and human hearing.
Let's analyze each statement:
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Statement 1: The response of the ear to the sound of increasing intensity is approximately logarithmic.
This statement is correct. The human ear perceives loudness on a scale that is roughly proportional to the logarithm of the sound intensity. This is why the decibel (dB) scale, which is logarithmic, is used to measure sound intensity levels. A large increase in intensity is perceived as a smaller increase in loudness.
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Statement 2: The sensitivity of the human ear does not vary with the frequency of the sound.
This statement is incorrect. The sensitivity of the human ear varies significantly with the frequency of the sound. The ear is most sensitive to frequencies between approximately 2 kHz and 5 kHz. Sensitivity decreases for frequencies much lower or higher than this range. This variation is represented by equal-loudness contours (like the Fletcher-Munson curves), which show the sound pressure level required for different frequencies to be perceived as equally loud.
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Statement 3: When two or more waves traverse the same medium, the displacement of any element of the medium is the algebraic sum of the displacements due to each wave.
This statement is correct. This is the principle of superposition, which applies to waves. When multiple waves are present in the same location at the same time, the resulting displacement of the medium is the vector sum (or algebraic sum for displacement in one dimension) of the displacements caused by each individual wave.
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Statement 4: Longitudinal waves can travel in all media - Solids, Liquids, and Gases.
This statement is correct. Longitudinal waves, where the particles of the medium oscillate parallel to the direction of wave propagation, can travel through solids, liquids, and gases because all these states of matter can sustain compression and expansion. Sound waves are a primary example of longitudinal waves that travel through these media.
Based on the analysis, Statement 2 is the one that is not correct.
Explanation of Incorrect Statement: Human Ear Sensitivity and Frequency
The human ear's sensitivity is indeed dependent on the frequency of the sound. We do not perceive sounds of the same intensity level equally loud if they have different frequencies. For instance, a sound at 100 Hz might need to be much more intense (higher dB level) than a sound at 3 kHz to be perceived with the same loudness. This variation in sensitivity is crucial for understanding how we perceive different sounds in our environment.
In summary:
| Statement | Correctness | Reason |
|---|---|---|
| Ear response to intensity is logarithmic | Correct | Basis of the dB scale; reflects how loudness is perceived. |
| Ear sensitivity does not vary with frequency | Incorrect | Ear sensitivity is highly frequency-dependent (e.g., most sensitive around 2-5 kHz). |
| Principle of superposition for waves | Correct | Displacements add up algebraically when waves overlap. |
| Longitudinal waves travel in S, L, G | Correct | Solids, liquids, and gases can support compression/expansion required for longitudinal waves like sound. |
Therefore, the statement that is not correct is that the sensitivity of the human ear does not vary with the frequency of the sound.
Revision Table: Key Concepts in Sound and Hearing
| Concept | Description | Relevance to Question |
|---|---|---|
| Logarithmic Intensity Response | Perception of loudness is logarithmic with respect to intensity (measured in Watts/m²). | Explains Statement 1. |
| Frequency-Dependent Sensitivity | Human ear's ability to detect sound varies with frequency. Different frequencies need different intensity levels to be heard or perceived as equally loud. | Explains why Statement 2 is incorrect. |
| Principle of Superposition | When waves meet, the resulting displacement is the sum of individual displacements. | Explains Statement 3. |
| Longitudinal Waves | Waves where particle motion is parallel to wave propagation. Sound is a common example. | Explains Statement 4. |
| Media for Longitudinal Waves | These waves require a medium that can be compressed and expanded, like solids, liquids, and gases. | Further explains Statement 4. |
Additional Information: Human Auditory Perception
Human hearing is a complex process involving the ear and the brain. The range of frequencies a typical human can hear is roughly from 20 Hz to 20,000 Hz, although this range shrinks with age, especially at higher frequencies.
Loudness is the subjective perception of sound pressure level. Pitch is the subjective perception of frequency. Timbre is the subjective perception of the quality of a sound, which helps distinguish between different types of sound production (e.g., different musical instruments playing the same note).
The non-linear response of the ear to intensity and the frequency-dependent sensitivity are adaptations that allow us to perceive a wide range of sound levels and frequencies in our environment effectively.
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