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A source of constant output power is used to generate a sound which is measured using a sound meter - AQA - A-Level Physics - Question 4 - 2018 - Paper 5
Question 4
A source of constant output power is used to generate a sound which is measured using a sound meter. The dashed line in Figure 3 shows the intensity level curve ove... show full transcript
Worked Solution & Example Answer:A source of constant output power is used to generate a sound which is measured using a sound meter - AQA - A-Level Physics - Question 4 - 2018 - Paper 5
Step 1
Discuss whether the dBA curve drawn is correct.
Answer
To determine the correctness of the dBA curve sketched by the student, we must understand the characteristics of dBA weighting compared to dB.
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Frequency Sensitivity: The ear's sensitivity starts low, rises to a maximum around 1 kHz, and then falls again. The maximum sensitivity of the ear occurs at this frequency range.
- At low frequencies (below 1 kHz), the intensity level is less perceptible, while at around 1 kHz, human hearing perceives sound most effectively.
- This means both scales should show a significant response at 1 kHz, but the dBA curve should demonstrate a more pronounced drop-off for frequencies below 1 kHz compared to the regular dB curve.
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dBA Maximum Value: The student's dBA curve suggests a maximum value that does not exceed 4 kHz, which is incorrect. It should approach a peak and then decline, reflecting the maximum sensitivity of the human ear. The student appears to indicate a plateau, which is incorrect as per actual sensitivity curves.
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Comparison against the dB Curve: While comparing the dashed dB curve, the dBA should closely follow it but exhibit a more pronounced decline in lower frequencies, categorically distinguishing itself from the dB curve.
In conclusion, while the student’s curve shows some correlation, it misrepresents the sensitivity characteristics of human hearing by not adhering to the expected pattern of the dBA curve relative to the dB curve.