Adiabatic Compression

  • ideal gas internal energy engine
    • assignment Bottle in a Bottle 2

      assignment Homework

      Bottle in a Bottle 2
      heat entropy ideal gas Energy and Entropy 2021 (2 years)

      Consider the bottle in a bottle problem in a previous problem set, summarized here.

      A small bottle of helium is placed inside a large bottle, which otherwise contains vacuum. The inner bottle contains a slow leak, so that the helium leaks into the outer bottle. The inner bottle contains one tenth the volume of the outer bottle, which is insulated.

      The volume of the small bottle is 0.001 m23 and the volume of the big bottle is 0.01 m3. The initial state of the gas in the small bottle was \(p=106\) Pa and its temperature \(T=300\) K. Approximate the helium gas as an ideal gas of equations of state \(pV=Nk_BT\) and \(U=\frac32 Nk_BT\).

      1. How many molecules of gas does the large bottle contain? What is the final temperature of the gas?

      2. Compute the integral \(\int \frac{{\mathit{\unicode{273}}} Q}{T}\) and the change of entropy \(\Delta S\) between the initial state (gas in the small bottle) and the final state (gas leaked in the big bottle).

      3. Discuss your results.

    • assignment Free Expansion

      assignment Homework

      Free Expansion
      Energy and Entropy 2021 (2 years)

      The internal energy is of any ideal gas can be written as \begin{align} U &= U(T,N) \end{align} meaning that the internal energy depends only on the number of particles and the temperature, but not the volume.*

      The ideal gas law \begin{align} pV &= Nk_BT \end{align} defines the relationship between \(p\), \(V\) and \(T\). You may take the number of molecules \(N\) to be constant. Consider the free adiabatic expansion of an ideal gas to twice its volume. “Free expansion” means that no work is done, but also that the process is also neither quasistatic nor reversible.
      1. What is the change in entropy of the gas? How do you know this?

      2. What is the change in temperature of the gas?

    • assignment Heat capacity of vacuum

      assignment Homework

      Heat capacity of vacuum
      Heat capacity entropy Thermal and Statistical Physics 2020
      1. Solve for the heat capacity of a vacuum, given the above, and assuming that photons represent all the energy present in vacuum.
      2. Compare the heat capacity of vacuum at room temperature with the heat capacity of an equal volume of water.
    • group Heat capacity of N$_2$

      group Small Group Activity

      30 min.

      Heat capacity of N2
      Contemporary Challenges 2022 (3 years)

      equipartition quantum energy levels

      Students sketch the temperature-dependent heat capacity of molecular nitrogen. They apply the equipartition theorem and compute the temperatures at which degrees of freedom “freeze out.”
    • face Fermi and Bose gases

      face Lecture

      120 min.

      Fermi and Bose gases
      Thermal and Statistical Physics 2020

      Fermi level fermion boson Bose gas Bose-Einstein condensate ideal gas statistical mechanics phase transition

      These lecture notes from week 7 of Thermal and Statistical Physics apply the grand canonical ensemble to fermion and bosons ideal gasses. They include a few small group activities.
    • assignment Isothermal/Adiabatic Compressibility

      assignment Homework

      Isothermal/Adiabatic Compressibility
      Energy and Entropy 2021 (2 years)

      The isothermal compressibility is defined as \begin{equation} K_{T}=-\frac{1}{V} \left(\frac{\partial V}{\partial p}\right)_{T} \end{equation} \(K_T\) is be found by measuring the fractional change in volume when the the pressure is slightly changed with the temperature held constant. In contrast, the adiabatic compressibility is defined as \begin{equation} K_{S}=-\frac{1}{V} \left(\frac{\partial V}{\partial p}\right)_{S} \end{equation} and is measured by making a slight change in pressure without allowing for any heat transfer. This is the compressibility, for instance, that would directly affect the speed of sound. Show that \begin{equation} \frac{K_{T}}{K_{S}} = \frac{C_{p}}{C_{V}} \end{equation} Where the heat capacities at constant pressure and volume are given by \begin{align} C_{p} &= T \left(\frac{\partial S}{\partial T}\right)_{p} \\ C_{V} &= T \left(\frac{\partial S}{\partial T}\right)_{V} \end{align}

    • assignment Nucleus in a Magnetic Field

      assignment Homework

      Nucleus in a Magnetic Field
      Energy and Entropy 2021 (2 years)

      Nuclei of a particular isotope species contained in a crystal have spin \(I=1\), and thus, \(m = \{+1,0,-1\}\). The interaction between the nuclear quadrupole moment and the gradient of the crystalline electric field produces a situation where the nucleus has the same energy, \(E=\varepsilon\), in the state \(m=+1\) and the state \(m=-1\), compared with an energy \(E=0\) in the state \(m=0\), i.e. each nucleus can be in one of 3 states, two of which have energy \(E=\varepsilon\) and one has energy \(E=0\).

      1. Find the Helmholtz free energy \(F = U-TS\) for a crystal containing \(N\) nuclei which do not interact with each other.

      2. Find an expression for the entropy as a function of temperature for this system. (Hint: use results of part a.)

      3. Indicate what your results predict for the entropy at the extremes of very high temperature and very low temperature.

    • group Heat and Temperature of Water Vapor (Remote)

      group Small Group Activity

      5 min.

      Heat and Temperature of Water Vapor (Remote)

      Thermo Heat Capacity Partial Derivatives

      In this introduction to heat capacity, students determine a derivative that indicates how much the internal energy changes as the temperature changes when volume is held constant.
    • assignment Potential energy of gas in gravitational field

      assignment Homework

      Potential energy of gas in gravitational field
      Potential energy Heat capacity Thermal and Statistical Physics 2020 Consider a column of atoms each of mass \(M\) at temperature \(T\) in a uniform gravitational field \(g\). Find the thermal average potential energy per atom. The thermal average kinetic energy is independent of height. Find the total heat capacity per atom. The total heat capacity is the sum of contributions from the kinetic energy and from the potential energy. Take the zero of the gravitational energy at the bottom \(h=0\) of the column. Integrate from \(h=0\) to \(h=\infty\). You may assume the gas is ideal.
    • face Review of Thermal Physics

      face Lecture

      30 min.

      Review of Thermal Physics
      Thermal and Statistical Physics 2020

      thermodynamics statistical mechanics

      These are notes, essentially the equation sheet, from the final review session for Thermal and Statistical Physics.
  • Energy and Entropy 2020

    A diesel engine requires no spark plug. Rather, the air in the cylinder is compressed so highly that the fuel ignites spontaneously when sprayed into the cylinder.

    In this problem, you may treat air as an ideal gas, which satisfies the equation \(pV = Nk_BT\). You may also use the property of an ideal gas that the internal energy depends only on the temperature \(T\), i.e. the internal energy does not change for an isothermal process. For air at the relevant range of temperatures the heat capacity at fixed volume is given by \(C_V=\frac52Nk_B\), which means the internal energy is given by \(U=\frac52Nk_BT\).

    Note: in this problem you are expected to use only the equations given and fundamental physics laws. Looking up the formula in a textbook is not considered a solution at this level.

    1. If the air is initially at room temperature (taken as \(20^{o}C\)) and is then compressed adiabatically to \(\frac1{15}\) of the original volume, what final temperature is attained (before fuel injection)?

    2. By what factor does the pressure increase?