For a magnetic system held at constant T and H (see Problem 1), the quantity that is minimized is the magnetic analogue of the Gibbs free energy, which obeys the thermodynamic identity
Phase diagrams for two magnetic systems are shown in Figure 5.14; the vertical axis on each of these figures is μ0H.
(a) Derive an analogue of the Clausius-Clapeyron relation for the slope of a phase boundary in the H-T plane. Write your equation in terms of the difference in entropy between the two phases.
(b) Discuss the application of your equation to the ferromagnet phase diagram in Figure 5.14.
(c) In a type-I superconductor, surface currents flow in such a way as to completely cancel the magnetic field (B, not H) inside. Assuming that M is negligible when the material is in its normal (non-superconducting) state, discuss the application of your equation to the superconductor phase diagram in Figure 5.14. Which phase has the greater entropy? What happens to the difference in entropy between the phases at each end of the phase boundary?
The enthalpy and Gibbs free energy, as defined in this section, give Special treatment to mechanical (compression-expansion) work, – P dV. Analogous quantities can be defined for other kinds of work, for instance, magnetic work. Consider the situation shown in below Figure, where a long solenoid [N turns, total length L) surrounds a magnetic specimen (perhaps a paramagnetic solid). If the magnetic field inside the specimen is and its total magnetic moment is , then we define an auxiliary field (often called simply the magnetic field) by the relation
where μo is the “permeability of free space,” 4π × 10–7 N/A2. Assuming cylindrical symmetry, all vectors must point either left of right, so we can drop the symbols and agree that rightward is positive, leftward negative. From Ampere’s law, one can also show that when the current in the wire is I, the H field inside the solenoidis NI/L, whether or not the specimen is present.
(a) Imagine making an infinitesimal change in the current in the wire, resulting in infinitesimal changes in B, M, and H. Use Faraday’s law to show that the work required (from the power supply) to accomplish this change is Wtotal = VHdB. (Neglect the resistance of the wire.)
(b) Rewrite the result of part (a) in terms of H and M, then subtract off the work that would be required even if the specimen wore not present. If we define W, the work done on the system J to be what’s left, show that W = μoHdM.
(c) What is the thermodynamic identity for this system? (Include magnetic work but not, mechanical work or particle flow.)
(d) How would you define analogues of the enthalpy and Gibbs free energy for a magnetic system? (The Helmholtz free energy is defined in the same way as for a mechanical system.) Derive the thermodynamic identities for each of these quantities, and discuss their interpretations.
Figure 1: A long solenoid, surrounding a magnetic specimen, connected to a power supply that can change the current, performing magnetic work.
Intro to Social Work Profession 3100-Summer 2016 What’s a Profession o Requires extensive training of an intellectual character o Services are vital to society’s well-being o Practitioners usually have a high degree of autonomy in deciding how to carry out the job o Must undergo a process of certification or licensing by the state in order to be eligible to carry out certain tasks or provide certain services How is Social Work a Profession o It meets all the criteria of a profession, particularly with regard to promoting the well-being of individuals and society as a whole o Historically, social workers have viewed the world through a unique conceptual lens