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A standing wave with a frequency of 1100 \(\mathrm{Hz}\) in a column of methane \(\left(\mathrm{CH}_{4}\right)\) at \(20.0^{\circ} \mathrm{C}\) produces nodes that are 0.200 \(\mathrm{m}\) apart. What is the value of \(\gamma\) for methane? (The molar mass of methane is 16.0 \(\mathrm{g} / \mathrm{mol}\) )

Short Answer

Expert verified
The value of \(\gamma\) for methane is approximately 1.27.

Step by step solution

01

Determine the speed of sound in methane

First, we need to find the speed of sound in the methane gas column using the wave relationship. We know that the distance between nodes is half the wavelength, that is \(d = \frac{\lambda}{2}\). Therefore, the wavelength \(\lambda = 2d = 2 \times 0.200\, \mathrm{m} = 0.400\, \mathrm{m}\). The speed of sound \(v\) can be calculated using \(v = f \cdot \lambda\), where \(f = 1100\, \mathrm{Hz}\). Substituting these values gives \(v = 1100 \times 0.400 = 440 \, \mathrm{m/s}\).
02

Calculate the value of \(\gamma\)

The speed of sound \(v\) in a gas is given by the formula \(v = \sqrt{\frac{\gamma \cdot R \cdot T}{M}}\), where \(R\) is the universal gas constant \(8.31\, \mathrm{J/mol\cdot K}\), \(T\) is the temperature in Kelvin (which is \(20.0^{\circ} C + 273 = 293\, K\)), and \(M\) is the molar mass of methane \(16.0\, \mathrm{g/mol}\) or \(0.016\, \mathrm{kg/mol}\). Rearrange the formula to solve for \(\gamma\): \(\gamma = \frac{v^2 \cdot M}{R \cdot T}\). Substituting the known values gives \(\gamma = \frac{(440)^2 \times 0.016}{8.31 \times 293}\).
03

Compute \(\gamma\)

Now, substitute the values to compute \(\gamma\):\[ \gamma = \frac{440^2 \times 0.016}{8.31 \times 293} = \frac{193600 \times 0.016}{2434.83} = \frac{3097.6}{2434.83} \approx 1.27 \].Thus, the value of \(\gamma\) for methane is approximately 1.27.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Standing Waves
Standing waves are a fascinating phenomenon in wave physics, occurring when two waves of the same frequency and amplitude move in opposite directions and intersect. This interaction creates a pattern of nodes (points of zero displacement) and antinodes (points of maximum displacement). In a column of gas, like methane, standing waves form when waves reflect back and forth between the ends of the container.
A useful feature of standing waves is that the distance between two successive nodes (or antinodes) is half of the wavelength of the wave. This property allows us to determine the wavelength of the wave when the distance between nodes is known. Understanding standing waves is crucial in applications like musical instruments, where sound waves resonate to create harmonics, and in scientific studies, where they help reveal properties of the medium through which they travel.
Wave Frequency
Wave frequency refers to the number of cycles a wave completes in one second, measured in Hertz (Hz). In the given problem, the wave frequency is 1100 Hz, meaning 1100 complete cycles occur every second. Frequency is a vital parameter because it remains constant regardless of changes in the medium through which the wave moves.
Frequency is directly related to wavelength and the speed of the wave through the formula \(v = f \cdot \lambda\), where \(v\) is the speed, \(f\) is the frequency, and \(\lambda\) is the wavelength. By knowing two of these quantities, the third can be easily calculated. Thus, the frequency of a wave helps determine how fast it propagates through a given medium and how long its waves are. This relationship is pivotal in acoustics, telecommunications, and many areas of physics.
Molar Mass
Molar mass is a fundamental chemical concept that represents the mass of one mole of a substance, expressed in grams per mole (g/mol). For gases, it helps in determining various properties such as the speed of sound through the gas.
In the context of the exercise, the molar mass of methane (CHâ‚„) is 16.0 g/mol, which is equivalent to 0.016 kg/mol when converted to be consistent with the units typically used in physics equations. Knowing the molar mass is essential when calculating phenomena such as the speed of sound in gases. It allows us to relate molecular weight to wave properties, facilitating the calculation of important material characteristics, such as the ratio of specific heats \(\gamma\).
Gas Constant
The gas constant, denoted as \(R\), is a crucial factor in thermodynamics and the ideal gas law. It is universally valued at 8.31 J/mol K. \(R\) provides a link between the properties of gases and their molecular characteristics.
In the formula for the speed of sound \(v = \sqrt{\frac{\gamma \cdot R \cdot T}{M}}\), it helps relate the pressure, volume, and temperature of a gas. The gas constant equates macroscopic properties of gases (pressure, volume, temperature) with the microscopic (moles), thereby bridging chemistry and physics.
Understanding how \(R\) integrates into sound speed calculations reveals how thermodynamic properties influence wave behaviors in gases. This insight is instrumental for fields that rely heavily on gas dynamics, such as meteorology and aerospace engineering.

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Most popular questions from this chapter

One type of steel has a density of \(7.8 \times 10^{3} \mathrm{kg} / \mathrm{m}^{3}\) and a breaking stress of \(7.0 \times 10^{3} \mathrm{N} / \mathrm{m}^{2}\) . A cylindrical guitar string is to be made of 4.00 \(\mathrm{g}\) of this steel. (a) What are the length and radius of the longest and thinnest string that can be placed under a tension of 900 \(\mathrm{N}\) without breaking? (b) What is the highest fundamental frequency that this string could have?

Horseshoe bats (genus Rhinolophus) emit sounds from their nostrils and then listen to the frequency of the sound reflected from their prey to determine the prey's speed. (The "horseshoe" that gives the hat its name is a depression around the nostrils that acts like a focusing mirror, so that the hat emits sound in a narrow beam like a flashlight.) A Rhinolophus flying at speed \(v_{\text { tot }}\) emits sound of fre-quency \(f_{\text { but }}\) ; the sound it hears reflected from an insect flying toward it has a higher frequency \(f_{\text { rent }}(\text { a) Show that the speed of the insect is }\) where \(v\) is the speed of sound. (b) If \(f_{\mathrm{bat}}=80.7 \mathrm{kHz}, \quad f_{\mathrm{rell}}=\) \(83.5 \mathrm{kHz},\) and \(v_{\mathrm{bat}}=3.9 \mathrm{m} / \mathrm{s},\) calculate the speed of the insect.

A swimming duck paddles the water with its feet once cvery 1.6 \(\mathrm{s}\) , producing surface waves with this period. The duck is moving at constant speed in a pond where the speed of surface waves is 0.32 \(\mathrm{m} / \mathrm{s}\) , and the crests of the waves ahead of the duck are spaced 0.12 \(\mathrm{m}\) apart. (a) What is the duck's speed? (b) How far apart are the crests behind the duck?

Standing sound waves are produced in a pipe that is 1.20 \(\mathrm{m}\) long. For the fundamental and first two overtones, determine the the locations along the pipe (measured from the left end) of the dis- placement nodes and the pressure nodes if (a) the pipe is open at both ends and (b) the pipe is closed at the left end and open at the right end.

The shock-wave cone created by the space shuttle at one instant during its reentry into the atmosphere makes an angle of \(58.0^{\circ}\) with its direction of motion. The speed of sound at this altitude is 331 \(\mathrm{m} / \mathrm{s}\) (a) What is the Mach number of the shuttle at this instant, and (b) how fast (in \(\mathrm{m} / \mathrm{s}\) and \(\mathrm{mi} / \mathrm{h} )\) is it traveling relative to the atmosphere? (c) What would be its Mach number and the angle of its shock-wave cone if it flew at the same speed but at low altitude where the speed of sound is 344 \(\mathrm{m} / \mathrm{s} ?\)

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