Chapter 3: Problem 88
Calculate the decibels associated with a doorbell if the intensity is \(I=1 \times 10^{-45} \mathrm{W} / \mathrm{m}^{2}\).
Short Answer
Expert verified
The decibels associated with the given intensity are -330 dB.
Step by step solution
01
Understanding the Decibel Formula
The decibel level, denoted as \( L \), is calculated using the formula: \[ L = 10 imes ext{log}_{10}\left(\frac{I}{I_0}\right) \] where \( I \) is the intensity we are given, and \( I_0 \) is the reference intensity, typically \( I_0 = 1 imes 10^{-12} \, \text{W/m}^2 \).
02
Substitute the Given Intensity
Plug the given intensity \( I = 1 imes 10^{-45} \,\text{W/m}^2 \) and the reference intensity \( I_0 = 1 imes 10^{-12} \, \text{W/m}^2 \) into the decibel formula: \[ L = 10 imes ext{log}_{10}\left(\frac{1 imes 10^{-45}}{1 imes 10^{-12}}\right) \].
03
Calculate the Ratio Inside the Logarithm
Calculate the fraction inside the logarithm: \[ \frac{1 \times 10^{-45}}{1 \times 10^{-12}} = 1 \times 10^{-33} \].
04
Compute the Logarithm
Find the logarithm of the ratio: \[ \text{log}_{10} (1 \times 10^{-33}) = -33 \] because \( \text{log}_{10}(10^{-33}) = -33 \).
05
Calculate the Decibel Level
Finally, substitute the logarithm result into the decibel formula: \[ L = 10 imes (-33) = -330 \]. So, the decibel level associated with this intensity is -330 dB.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Understanding Intensity
Intensity in sound refers to the amount of energy that a sound wave carries per unit area. It is expressed in watts per square meter (W/m²).
Think of intensity as how much power the sound is delivering to a surface. A higher intensity means more energy and a louder sound.
Some important points about intensity:
Think of intensity as how much power the sound is delivering to a surface. A higher intensity means more energy and a louder sound.
Some important points about intensity:
- It always decreases with distance from the sound source.
- Measured in a specific direction.
- High intensity can result in discomfort or even pain.
Logarithmic Scale for Sound
A logarithmic scale is used for measuring sound because of the vast range of sound intensities that can be heard by the human ear.
A logarithmic scale, as opposed to a linear one, allows us to compress these large differences into simpler numbers.
Key points about logarithmic scales:
A logarithmic scale, as opposed to a linear one, allows us to compress these large differences into simpler numbers.
Key points about logarithmic scales:
- They simplify calculations and comparisons.
- The base 10 logarithm is commonly used in sound measurement.
- Large changes in sound intensity correspond to smaller changes on a logarithmic scale.
Measuring Sound with Decibels
Sound is measured in decibels (dB), a unit that expresses the ratio of a given intensity to a reference intensity on a logarithmic scale.
The decibel formula is \( L = 10 \times \text{log}_{10}\left(\frac{I}{I_0}\right) \), where \( I \) is the intensity of the sound, and \( I_0 \) is the reference intensity.
Here's why decibels are handy:
The decibel formula is \( L = 10 \times \text{log}_{10}\left(\frac{I}{I_0}\right) \), where \( I \) is the intensity of the sound, and \( I_0 \) is the reference intensity.
Here's why decibels are handy:
- They make it easier to handle very large or very small numbers.
- No negative sections exist on a logarithmic scale for human audibility.
- Provide a clearer understanding of the perceived loudness of sounds.
Role of Reference Intensity in Sound Measurement
Reference intensity \( I_0 \) is crucial when converting a sound intensity to decibels.
It's the baseline or starting point for measuring sound intensity, usually set at \( 1 \times 10^{-12} \) W/m².
Aspects of reference intensity include:
It's the baseline or starting point for measuring sound intensity, usually set at \( 1 \times 10^{-12} \) W/m².
Aspects of reference intensity include:
- It represents the threshold of hearing for the average human ear.
- Allows comparison of different sound intensities on a consistent scale.
- Serves as a fixed point to relate other sound measurements.