A point source of sound has a power of 17 W. Calculate, in dB, the intensity level at a distance of 12 m from the source. intensity level = ____________ dB The frequency of a sound is increased from 3.0 kHz to 8.0 kHz with no change in intensity. One change in the sound perceived by a person with normal hearing is an increase in pitch. Explain one other change to the sound perceived by the person as the frequency is increased from 3.0 kHz.

A-Level AQA Physics Thermal Energy Transfer: A point source of sound has a po

A point source of sound has a power of 17 W - AQA - A-Level Physics - Question 3 - 2021 - Paper 5

Question 3

A point source of sound has a power of 17 W. Calculate, in dB, the intensity level at a distance of 12 m from the source. intensity level = ____________ dB The fr... show full transcript

Worked Solution & Example Answer:A point source of sound has a power of 17 W - AQA - A-Level Physics - Question 3 - 2021 - Paper 5

Step 1

Calculate the Area

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Answer

To find the intensity of the sound, first calculate the area over which the sound propagates. For a point source, the surface area (A) at a distance (r) is given by:

$A = 4 \pi r^2$

Substituting the given distance of 12 m:

$A = 4 \pi (12^2) \approx 452.39 \text{ m}^2$

Step 2

Calculate the Intensity

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Answer

Next, calculate the intensity (I) of the sound using the formula:

$I = \frac{P}{A}$

Where P is the power (17 W) and A is the area calculated:

$I = \frac{17}{452.39} \approx 0.0376 \text{ W/m}^2$

Step 3

Calculate the Intensity Level

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Finally, calculate the intensity level in decibels (dB) using the formula:

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

where $I_0 = 10^{-12} \text{ W/m}^2$ (reference intensity). Thus:

$L = 10 \log_{10}\left( \frac{0.0376}{10^{-12}} \right) \approx 10 \log_{10}(3.76 \times 10^{10}) \approx 10 \times 10.576 \approx 105.76 ext{ dB}$

Step 4

One Other Change in Sound Perception

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Answer

As the frequency is increased from 3.0 kHz to 8.0 kHz, one other change perceived by a person is that the sound may become quieter at higher frequencies. This phenomenon occurs because human hearing sensitivity varies with frequency, often being less sensitive as frequency increases.

A point source of sound has a power of 17 W - AQA - A-Level Physics - Question 3 - 2021 - Paper 5

Worked Solution & Example Answer:A point source of sound has a power of 17 W - AQA - A-Level Physics - Question 3 - 2021 - Paper 5

Calculate the Area

Calculate the Intensity

Calculate the Intensity Level

One Other Change in Sound Perception

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