Chapter 23: Problem 6
What is the speed of compression waves (sound waves) in water? The bulk modulus for water is \(2.2 \times 10^{9} \mathrm{~N} / \mathrm{m}^{2}\). $$ v=\sqrt{\frac{\text { Bulk modulus }}{\text { Density }}}=\sqrt{\frac{2.2 \times 10^{9} \mathrm{~N} / \mathrm{m}^{2}}{1000 \mathrm{~kg} / \mathrm{m}^{3}}}=1.5 \mathrm{~km} / \mathrm{s} $$
Short Answer
Step by step solution
Understand the Formula
Identify the Given Values
Plug Values into the Formula
Simplify the Calculation
Calculate the Speed
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Bulk Modulus
The formula for bulk modulus, denoted as \( B \), is \( B = -V \frac{\Delta P}{\Delta V} \) where \( V \) is the volume, \( \Delta P \) is the change in pressure, and \( \Delta V \) is the change in volume as a result of that pressure.
- Units: Bulk modulus is expressed in pascals \( (\text{Pa}) \), which is equivalent to \( \text{N}/\text{m}^2 \).
- Physical Insight: A higher bulk modulus indicates that the material is difficult to compress; it responds less to pressure changes, which is a crucial factor in wave propagation.
Density of Water
- Role in Sound Transmission: Density directly affects the speed of sound in a medium because sound waves move through mediums by vibrating particles; the more closely packed these particles are, the faster sound can travel.
- Impact on Calculation: Having a consistent density allows for predicting how sound waves behave in water, which is essential when calculating the wave speed using the formula \( v = \sqrt{\frac{B}{\rho}} \).
Physics Problem Solving
- Identify Given Variables: Write down what you know and what needs to be calculated. Look for units and convert them if necessary to ensure consistency across the calculation.
- Use Relevant Formulas: Every aspect of physics has specific formulas designed to interrelate variables. Here, we're focusing on the formula for wave speed in a medium, \( v = \sqrt{\frac{B}{\rho}} \), where solving involves algebraic manipulation and logical thinking.
- Step-by-step Calculation: Plug known values into the formula and simplify step-by-step, as demonstrated in the detailed solution.
Wave Speed Calculation
- Insert Known Values: The bulk modulus \( B \) and density \( \rho \) of water have predefined values: \( B = 2.2 \times 10^9 \text{ N/m}^2 \) and \( \rho = 1000 \text{ kg/m}^3 \).
- Perform the Calculation: Substituting, we find \( v = \sqrt{\frac{2.2 \times 10^9}{1000}} \). First, perform the division inside the square root, giving \( 2.2 \times 10^6 \). Then, the square root of this value gives us approximately \( 1483 \mathrm{~m/s} \), or converted, \( 1.5 \mathrm{~km/s} \).