THermodynamics of a magnetic system

[Feynmanfan]

I've been given the fundamental equation of a magnetic system .U(S,N,I)=...
I have to calculate some thermodynamic potentials such as U[T] etc.

One of them is the so called magnetic enthalpy and the expression for it is
U[p,B]. Another one is U[p]. How do I calculate it? I don't even know what it means.

Since I'm only used to pression, volume etc. I don't know what p is.

If S is entropy, I the equivalent of volume and B (magnetic field or whatever) the equivalent of pressure. WHat is p?

 

[Andrew Mason]

Since I'm only used to pression, volume etc. I don't know what p is.

If S is entropy, I the equivalent of volume and B (magnetic field or whatever) the equivalent of pressure. WHat is p?

You haven't exactly explained the question very well.

Generally magnetic enthalpy is a state variable that will indicate whether the magnetic energy of the system (internal magnetic energy + magnetic work) has increased or decreased. It is just that there are different definitions of work and internal energy for a magnetic system (depending on what kind of magnetic system it is) than for an ideal gas system. You can have paramagnetic low temperature gases, paramagnetic solids, magnetic solids, nuclear magnetic or magnetic ion systems, or composite paramagnetic systems consisting of magnetic solids and gases. They have different parameters for work and internal energy.

AM

 

[Graeme Robinson]

The thermodynamics of a magnetic system can be quite complex, but understanding the fundamental equation and thermodynamic potentials can help make it more manageable. Let's break down the different components of the equation to better understand how to calculate the thermodynamic potentials.

First, the fundamental equation for a magnetic system is U(S,N,I), where U represents the internal energy, S is the entropy, N is the number of particles, and I is the magnetic moment. This equation relates the internal energy of the system to its entropy, number of particles, and magnetic moment.

Now, let's look at the two specific thermodynamic potentials mentioned - magnetic enthalpy and U[p]. The magnetic enthalpy, denoted as U[p,B], is a function of both pressure (p) and magnetic field (B). This means that it takes into account the effects of both pressure and magnetic field on the system's internal energy. To calculate this, you would need to know the values of p and B at a specific temperature.

On the other hand, U[p] is a function of only pressure (p) and does not take into account the magnetic field. This means that it measures the change in internal energy of the system due to changes in pressure alone. To calculate this, you would need to know the value of p at a specific temperature.

In thermodynamics, pressure (p) is a measure of the force exerted on a unit area of the system. It is usually represented in units of pascals (Pa) or atmospheres (atm). In the context of a magnetic system, pressure can be thought of as the external pressure applied to the system or the pressure exerted by the magnetic field on the system.

In summary, to calculate the thermodynamic potentials in a magnetic system, you would need to know the values of pressure (p) and magnetic field (B) at a specific temperature. Understanding the fundamental equation and the role of each variable in it can help in making these calculations.