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In a certain particle accelerator, protons travel around a circular path of diameter \(23.0 \mathrm{~m}\) in an evacuated chamber, whose residual gas is at \(295 \mathrm{~K}\) and \(1.00 \times 10^{-6}\) torr pressure. (a) Calculate the number of gas molecules per cubic centimeter at this pressure. (b) What is the mean free path of the gas molecules if the molecular diameter is \(2.00 \times 10^{-8} \mathrm{~cm} ?\)

Short Answer

Expert verified
(a) Approximately \(3.29 \times 10^{10}\) molecules/cm³. (b) Mean free path is approximately \(6.0 \times 10^{-2} \) m.

Step by step solution

01

Convert Pressure to Pascals

The given pressure is in torr. To convert it to Pascals (Pa), we use the conversion factor: \(1 ext{ torr} = 133.322 ext{ Pa}\). Thus, the pressure in Pascals is: \(1.00 \times 10^{-6} ext{ torr} \times 133.322 ext{ Pa/torr} = 1.33322 \times 10^{-4} ext{ Pa}\).
02

Use Ideal Gas Law to Find Molecules per Cubic Meter

The ideal gas law can be rearranged to find the number of molecules per volume: \(n = \frac{P}{kT}\), where \(P\) is the pressure, \(k = 1.38 \times 10^{-23} \, \text{J/K} \) is the Boltzmann constant, and \(T = 295 \, \text{K} \) is the temperature. Substitute the values: \(n = \frac{1.33322 \times 10^{-4}}{1.38 \times 10^{-23} \times 295}\). Calculate to find \(n\).
03

Calculate Molecules per Cubic Centimeter

Convert the result from Step 2 from molecules per cubic meter to molecules per cubic centimeter by dividing by \(10^6\). This gives us the number of molecules per cubic centimeter at the given pressure and temperature.
04

Find Mean Free Path

The mean free path \(\lambda\) can be calculated using the formula \(\lambda = \frac{kT}{\sqrt{2} \pi d^2 P}\), where \(d = 2.00 \times 10^{-8} \text{ cm} = 2.00 \times 10^{-10} \text{ m}\). Substitute the values for \(k, T, P,\) and \(d\) into the formula and calculate \(\lambda\).

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Key Concepts

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

Particle Accelerator
Particle accelerators are fascinating devices used to propel charged particles, such as protons, to high speeds and energies. These machines work by using electromagnetic fields to accelerate and direct these particles along a defined path, which is often circular. Accelerators are essential tools in physics research, allowing scientists to explore the fundamental properties of matter.

Inside the accelerator, it's crucial to maintain a vacuum environment to prevent particles from colliding with gas molecules. Even the tiniest amount of residual gas, such as that with pressure as low as 1.00 × 10^{-6} torr, can influence the behavior and travel path of particles.

This concept is important when considering experiments that involve precise measurements, as interactions with even trace gases can alter results.
Ideal Gas Law
The Ideal Gas Law is a fundamental equation in chemistry and physics used to relate the properties of gases: pressure ( P ), volume ( V ), temperature ( T ), and the number of moles ( n ). Its formula is: PV = nRT , where R is the universal gas constant.

In many physics problems, like those involving particle accelerators, we use a modified version: PV = NkT . Here, N is the number of molecules and k is the Boltzmann constant. This variation is particularly helpful when dealing with gaseous particles in specified volumes and under varying temperatures and pressures.

In the study scenario, we used this law to convert the low pressure in the accelerator into a more comprehensible number of molecules per cubic centimeter. Understanding how to manipulate this equation is essential for dealing with real-world applications involving gases.
Molecular Diameter
Molecular diameter is a term referring to the size of a molecule. It is crucial when calculating interactions between molecules, such as collisions.

The diameter of a molecule affects its mean free path, which is the average distance a molecule travels before colliding with another. In this educational exercise, the diameter is given as 2.00 × 10^{-8} cm, a common size for diatomic molecules like nitrogen or oxygen.

Knowing the molecular diameter enables us to calculate the mean free path. With a larger molecule, collisions occur more frequently, reducing the path length. This concept helps in predicting gas behavior under different conditions, essential in controlled environments like particle accelerators.
Boltzmann Constant
The Boltzmann constant ( k ) is a fundamental constant that connects temperature with energy at the particle level. Its value is approximately 1.38 × 10^{-23} J/K.

In physics, it acts as a bridge between macroscopic and microscopic worlds, linking the temperature of a gas to the kinetic energy of its molecules. Within the framework of the Ideal Gas Law, it allows us to understand how many molecules are in a certain volume at a specified temperature and pressure.

When calculating the mean free path of molecules in a gas, the Boltzmann constant helps us relate the effects of temperature and molecular size on how far molecules can travel before colliding. This constant is key in many calculations involving gases, influencing everything from theoretical physics to practical applications in industrial processes.

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Most popular questions from this chapter

During a compression at a constant pressure of \(250 \mathrm{~Pa},\) the volume of an ideal gas decreases from \(0.80 \mathrm{~m}^{3}\) to \(0.20 \mathrm{~m}^{3}\). The initial temperature is \(360 \mathrm{~K},\) and the gas loses \(210 \mathrm{~J}\) as heat. What are (a) the change in the internal energy of the gas and (b) the final temperature of the gas?

An ideal gas with \(3.00 \mathrm{~mol}\) is initially in state 1 with pressure \(p_{1}=20.0 \mathrm{~atm}\) and volume \(V_{1}=1500 \mathrm{~cm}^{3} .\) First it is taken to state 2 with pressure \(p_{2}=1.50 p_{1}\) and volume \(V_{2}=2.00 V_{1} .\) Then it is taken to state 3 with pressure \(p_{3}=2.00 p_{1}\) and volume \(V_{3}=0.500 V_{1} .\) What is the temperature of the gas in (a) state 1 and (b) state \(2 ?\) (c) What is the net change in internal energy from state 1 to state \(3 ?\)

A container holds a mixture of three nonreacting gasesi\(2.40 \mathrm{~mol}\) of gas 1 with \(C_{V 1}=12.0 \mathrm{~J} / \mathrm{mol} \cdot \mathrm{K}, 1.50 \mathrm{~mol}\) of gas 2 with \(C_{V_{2}}=12.8 \mathrm{~J} / \mathrm{mol} \cdot \mathrm{K},\) and \(3.20 \mathrm{~mol}\) of gas 3 with \(C_{V 3}=20.0 \mathrm{~J} / \mathrm{mol} \cdot \mathrm{K}\) What is \(C_{V}\) of the mixture?

Suppose \(1.00 \mathrm{~L}\) of a gas with \(\gamma=1.30\), initially at \(273 \mathrm{~K}\) and \(1.00 \mathrm{~atm},\) is suddenly compressed adiabatically to half its initial volume. Find its final (a) pressure and (b) temperature. (c) If the gas is then cooled to \(273 \mathrm{~K}\) at constant pressure, what is its final volume?

Compute (a) the number of moles and (b) the number of molecules in \(1.00 \mathrm{~cm}^{3}\) of an ideal gas at a pressure of \(100 \mathrm{~Pa}\) and a temperature of \(220 \mathrm{~K}\).

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