Questions on phase space and CanonicalMicrocanonical ensembles

In summary, the conversation covers topics related to phase space, trajectory, density of states, entropy, temperature, energy, and ensembles. It includes discussions on the sketching of a weight free falling trajectory, calculating density of states for a 1 dimensional lattice model, and the differences between canonical and microcanonical ensembles. The conversation also mentions the relationship between Ω (number of microstates) and Ω' (density of states). The speaker also expresses uncertainty and requests clarification on certain aspects of the problems.
  • #1
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1. Sketch the phase space of a weight free falling along the z coordinate (no
motion in other directions). Sketch the trajectory of the free fall including
impact on the ground.
2. Calculate the density of states, entropy, and temperature (all as a function of
energy) for the following model: Consider a 1 dimensional lattice with 3 elds
(periodic boundary conditions). Every lattice site can have the states ; 0; +.
Interaction energies are only between nearest neighbors and are E() = +4
E(++) = +3 E(+) = E(+) = 2 everything else E = 0. Sketch the highest
and lowest energy states.
3. Dierences: CanonicalMicrocanonical ensemble
Assume you have given a density of states as a function of energy
(E). This can be used to calculate canonical and microcanonical data.
(a) Discretize Energy in units of E and write down the entropy microcanoni-
cally.
(b) Give the partition sum in the canonical and the microcanonical ensemble
(as a function of the relevant observables).
(c) Assume you measure an observable as a function of energy A(E). Write
down its average canonically and microcanonically.

2.
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3. I don't know how to sketch in problem 1 and for problem 2, I think maybe there are mistakes in the problem, otherwise, the highest energy should be +∞ and the lowest is -∞. Problem 3 I totally have no idea of it, and I want to know the difference and relation between Ω(the number of microstates) and Ω'(the density of states).
 
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  • #2
Do you know the definitions of any of those things? Whoever gave you this problem certainly expects you to know them.

(And this problem is physics, not mathematics, so I am moving it.)
 

1. What is phase space in the context of statistical mechanics?

Phase space in statistical mechanics is a mathematical space that represents all possible states of a physical system. It is a multi-dimensional space where each point represents a set of coordinates that describe the state of the system, such as position and momentum of particles.

2. What are the differences between canonical and microcanonical ensembles?

The canonical ensemble is used to describe systems that exchange energy with their surroundings, while the microcanonical ensemble is used for isolated systems with fixed energy. In the canonical ensemble, temperature is kept constant, while in the microcanonical ensemble, energy is held constant. Additionally, the canonical ensemble considers the system to be in equilibrium with a heat reservoir, while the microcanonical ensemble assumes the system is in equilibrium with itself.

3. How are phase space and ensembles related?

Phase space is used to represent the state of a system in the context of statistical mechanics, while ensembles are used to describe the statistical properties of a system. Ensembles are defined in terms of phase space, as they represent a collection of points in phase space that satisfy certain constraints, such as fixed energy or temperature.

4. What is the significance of the partition function in statistical mechanics?

The partition function is a mathematical tool used in statistical mechanics to calculate the thermodynamic properties of a system. It is a sum over all possible states of the system in phase space, and it allows for the calculation of important quantities such as internal energy, entropy, and free energy. It is a key component in connecting microscopic properties of a system to its macroscopic behavior.

5. How do phase space and ensembles relate to the laws of thermodynamics?

Phase space and ensembles are used to describe the statistical behavior of a system, while the laws of thermodynamics govern the behavior of macroscopic systems. Phase space and ensembles provide a microscopic understanding of the thermodynamic properties of a system, and they can be used to derive the laws of thermodynamics. Additionally, the partition function, which is based on phase space and ensembles, allows for the calculation of thermodynamic quantities such as energy and entropy.

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