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Use a computer to produce a table and graph, like those in this section, for two interacting two-state paramagnets, each containing 100 elementary magnetic dipoles. Take a "unit" of energy to be the amount needed to flip a single dipole from the "up" state (parallel to the external field) to the "down" state (antiparallel). Suppose that the total number of units of energy, relative to the state with all dipoles pointing up, is \(80 ;\) this energy can be shared in any way between the two paramagnets. What is the most probable macrostate, and what is its probability? What is the least probable macrostate, and what is its probability?

Short Answer

Expert verified
The most probable macrostate has even energy distribution; the least probable has extreme imbalance.

Step by step solution

01

Define Parameters and Understand the System

We have two paramagnet systems, A and B, each consisting of 100 magnetic dipoles. The total energy is 80 units. By definition, each energy unit corresponds to flipping one dipole from the up state to the down state. The total number of dipoles (N) in each paramagnet is 100. Each system's possible states range from 0 to 100, where a state indicates the number of down dipoles.
02

Establish the Constraints

The energy unit constraint states that the total energy distributed between both paramagnets is 80 units. If system A has U_A units of energy, then system B's energy U_B = 80 - U_A. Therefore, we will evaluate each division of 80 energy units between the two systems to identify their macrostates.
03

Calculate Macrostate Probabilities

The number of ways (Ω) to arrange a given macrostate is determined by the multiplicity function: \( \Omega = \binom{N}{U} \), where \( \binom{N}{U} \) is the binomial coefficient for N choose U. Calculate Ω for each U_A from 0 to 80 and use \( \Omega(A) \times \Omega(B) \) to find the total multiplicity for that distribution.
04

Create Table and Graph

Create a table listing U_A, U_B, Ω(A), Ω(B), and \( \Omega = \Omega(A) \times \Omega(B) \) for all possible configurations. Use software like Excel or Python matplotlib to plot U_A against \( \Omega \). This helps visualize the probability distribution of macrostates.
05

Identify Most Probable Macrostate

Identify the macrostate with the highest multiplicity from the table. This macrostate is the most probable since it has the highest number of arrangements.
06

Identify Least Probable Macrostate

Similarly, identify the macrostate with the lowest multiplicity from the table. This macrostate is the least probable as it has the smallest number of arrangements.

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Key Concepts

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

Two-state Paramagnet
In thermal physics, a two-state paramagnet is a fascinating system that consists of many magnetic dipoles. Each dipole can be in one of two states:
  • An "up" state, where it aligns with an external magnetic field.
  • A "down" state, where it opposes the field.
All dips in the system can freely switch between these states. However, switching states requires energy. For instance, flipping a dipole from "up" to "down" requires one energy unit.
When considering a paramagnet with many dipoles, all possible combinations of "up" and "down" orientations form the basis for analyzing energy distributions and probabilities in the system. Two-state paramagnets serve as a key study in understanding microstates and macrostates of a thermal system.
Macrostate Probability
Macrostate probability refers to the likelihood of the system being in a particular arrangement of dipoles, characterized by a specific energy distribution. In our system of two paramagnets, each with 100 dipoles, the macrostate can be defined by how many dipoles are in the "down" state in each paramagnet.
Given the total energy constraint, the macrostate probability is determined by the multiplicity of that state. It reflects how many different ways we can arrange the dipoles to achieve a specific energy distribution between the two paramagnets. The most probable macrostate has the highest multiplicity, meaning there are more ways to achieve that energy distribution, making it a key outcome when analyzing such systems.
Energy Distribution
In thermal physics, energy distribution in a two-state paramagnet involves allocating the total units of energy among the dipoles. This distribution defines how many dipoles are in the "up" or "down" state within each paramagnet.
  • When a dipole flips from "up" to "down", it takes a unit of energy.
  • The total energy of 80 units can be shared in various ways between two paramagnets each having 100 dipoles.

The energy distribution impacts the probability distribution and multiplicity function. Understanding how energy is distributed provides insights into the most and least probable macrostates, helping predict the behavior of the system.
Probability Distribution
The probability distribution in a thermal physics context, such as our two-state paramagnet, helps in visualizing how likely different macrostates are. By computing the multiplicity for each possible energy distribution, we can create a probability distribution that shows which macrostates are most or least likely.
  • Using graphs, we can plot energy states against multiplicity to visually understand this distribution.
  • Typically, probability peaks at the most probable macrostate and declines for less probable macrostates.

This distribution aids in predicting how energy will likely distribute across different states in the paramagnetic system. It serves as a powerful tool for both theoretical and practical explorations of thermal phenomena.
Multiplicity Function
The multiplicity function is a crucial concept for calculating the number of ways to achieve a certain macrostate in a two-state paramagnet. It is defined using the binomial coefficient:\[ \Omega = \binom{N}{U} \]Here, \( N \) is the total number of dipoles, and \( U \) is the number of dipoles in the down state.
This function indicates how many ways you can arrange dipoles to achieve a particular distribution of energy among them. Higher multiplicity means there are more ways to distribute energy, leading to a higher probability of that macrostate.
By calculating \( \Omega(A) \) for paramagnet A and \( \Omega(B) \) for paramagnet B, you can then determine the total multiplicity \( \Omega = \Omega(A) \times \Omega(B) \). The multiplicity function is foundational for understanding the probability and distribution of energy states in thermal systems.

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Most popular questions from this chapter

Calculate the multiplicity of an Einstein solid with 30 oscillators and 30 units of energy. (Do not attempt to list all the microstates.)

For a single large two-state paramagnet, the multiplicity function is very sharply peaked about \(N_{\uparrow}=N / 2\) (a) Use Stirling's approximation to estimate the height of the peak in the multiplicity function. (b) Use the methods of this section to derive a formula for the multiplicity function in the vicinity of the peak, in terms of \(x \equiv N_{\uparrow}-(N / 2) .\) Check that your formula agrees with your answer to part (a) when \(x=0\) (c) How wide is the peak in the multiplicity function? (d) Suppose you flip 1,000,000 coins. Would you be surprised to obtain 501,000 heads and 499,000 tails? Would you be surprised to obtain 510,000 heads and 490,000 tails? Explain.

Rather than insisting that all the molecules be in the left half of a container, suppose we only require that they be in the leftmost \(99 \%\) (leaving the remaining \(1 \% \text { completely empty }) .\) What is the probability of finding such an arrangement if there are 100 molecules in the container? What if there are 10,000 molecules? What if there are \(10^{23} ?\)

Suppose you flip 20 fair coins. (a) How many possible outcomes (microstates) are there? (b) What is the probability of getting the sequence HTHHTTTHTHHHTHHHHTHT (in exactly that order)? (c) What is the probability of getting 12 heads and 8 tails (in any order)?

Consider a system of two Einstein solids, \(A\) and \(B\), each containing 10 oscillators, sharing a total of 20 units of energy. Assume that the solids are weakly coupled, and that the total energy is fixed. (a) How many different macrostates are available to this system? (b) How many different microstates are available to this system? (c) Assuming that this system is in thermal equilibrium, what is the probability of finding all the energy in solid \(A\) ? (d) What is the probability of finding exactly half of the energy in solid \(A\) ? (e) Under what circumstances would this system exhibit irreversible behavior?

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