**T. H. Tennahewa**

We specify the temp, T; by in here S means Entropy which details the way of measuring disorder in the system and U for Internal energy. In here x means the incomplete differentiation that should hold constant in the thermodynamic formula relating TdS and dU. this relation comes from the first law of Thermodynamics. That's;

;

We can establish heat with relating Enthalpy (H) also. That's in here too y stands for the partial differentiation which should hold continuous in the thermodynamic formula relating TdS and dH. Below is the derivation of above formula.

We called complete temps as a temperatures where on the Kelvin range 0 K as the definite zero point, where all action in a traditional gas would stop. Most systems, including a classical gas are limited to positive absolute temperatures. To become able to reach negative heat, a system must possess an upper bound for the of its particles, which is a maximal possible energy a particle of the system can have. This limit is no exterior limit in the sense that there is merely no more energy available. It is an interior limit - the particles cannot absorb more energy even when there is plenty available. It is important to notice that the negative temp region, with more of the atoms in the higher allowed energy state, is actually warmer than the positive heat region. If this technique were to be brought into connection with a system containing more atoms in a lesser energy condition (positive temperatures) warmth would stream from the system with the negative temperatures to the system with the positive conditions.

By this is of temperatures we can describe above body.

If the energy in the machine is minimum amount (Emin), all particles are in the lowest possible energy point out and the entropy is zero. The curve is vertical at this time with an infinite slope and temperature is therefore zero. When the energy raises, the particles start to take up higher energy state governments, and the entropy increases. You will find, however, always more allergens at low energies than at high energies this is same as the usual Boltzmann distribution. (Shape 2 below) The slope of the entropy versus energy curve lowers and the temperature therefore increases. At some point, when there will do energy in the system, the particles distribute equally over all energy states. Therefore the disorder and the entropy are maximum. The curve is completely flat at this time, with a slope of zero, and the temps is therefore infinite. If the total energy in the machine is further increased, more allergens will take up high energies than low energies this is identical to the inverted of the Boltzmann distribution. Because the energy circulation becomes narrower again, disorder and entropy starts off to decrease. This isn't a usual action because usually entropy rises with increasing energy. The slope of the curve is negative in this region and then the absolute temps is negative. When the energy in the system is maximum (Emax), all particles are at their maximum possible energy. The entropy is again zero. The curve is again vertical therefore the temp is again zero, but this time it is negative beliefs. Thus, while a temperatures of positive and negative infinity is in physical form identical, heat of positive and negative zero are extremely different. Because of that we could write temp range as +0 K, +300 K, . . . , + K, K, . . . , 300 K, . . . , 0 K.

Figure 2- The Maxwell- Boltzmann distribution

In the Carnot pattern of a high temperature engine heat utilized from the hot tank and heat turned down to the cold tank while work done by the system. In that case we specify the efficiency of the procedure as,

In here Q1 is a warmth absorbed at temperatures T1 and Q2 is a heating rejected at temperature T2. In heat engine motor T2 / T1 < 1, therefore efficiency is positive. But also for negative temps reservoirs T2 / T1 > 1, therefore efficiency is negative and can be quite large. In cases like this work has to be supplied to keep up the pattern.

It should be observed that whenever Carnot cycle is operated between two negative heat that is work is performed by the device while heat consumed from cold reservoir and declined to hot tank. Efficiency of the machine isn't just positive but additionally it is less than unity. Thus at both positive and negative temperatures cyclic heating engines which produce work have efficiencies less than unity that is they absorb more heat than produced work. Second law of thermodynamics should have to modify to use with this type of Carnot cycle. Within, entropy formulation and Clausius assertion continue to be unchanged and Kelvin-Plank formulation has to be changed. These are brought up below.

- Entropy formulation

The entropy of a system is a adjustable of its state and the entropy of isolated system can't ever decrease.

- Clausius Statement

It is impossible to construct a tool operating in a closed cycle that will produce no other impact than the copy of heat from a much cooler to hotter body.

- Kelvin- Plank formulation

It is impossible to construct an engine unit, which is operating in a cycle produces no other impact except to exterior heat from a single tank and do comparative amount of work.

Modified declaration:

It is impossible to create an engine motor that will operate in a shut circuit and produce no result other than the extraction of temperature from an optimistic temperature tank with the performance of your equal amount of work or the rejection of high temperature into a poor temperature tank with the equivalent work being done on the engine unit.

- Carathodory form

In any community of any point out there are states that can't be come to from it by an adiabatic process.

Both first and second regulations of thermodynamics can be used at negative temperature ranges as at positive ones to derive other thermodynamic relationships. From these laws and regulations it is interpreted that the issue of warming a hot system at negative temperatures is analogous to the issue in air conditioning a chilly system at positive temperature.

The important requirements for thermodynamical system to be able for negative heat range are:

- The components of the thermodynamical system must be in thermodynamical equilibrium among themselves in order to describe the machine by temp.
- There must be an upper limit of the possible energy of the allowed says of the system. It is need a lower bound for the power to be able to get positive heat and an top bound in order to get negative heat.
- The system must be thermally isolated from all systems which do not fulfill both of the above mentioned conditions.

To satisfy the next condition negative temperatures are to be achieved with a finite energy. In thermal equilibrium the number of elements in the mth state is proportional to the Boltzmann factor; here Wm is energy of the mth express.

Boltzmann circulation function which is shaped using Boltzmann factor is given below.

In negative heat circumstance when Wm enhances start Boltzmann factor increases exponentially therefore high energy states tend to be more occupied than low energy areas. As a result of this we're able to say that lacking any top limit to the vitality negative temperatures cannot be performed with a finite energy. Since most of the systems do not fulfill this conditions negative temperatures are occurs hardly ever.

Spin systems sometimes form the thermodynamic systems which can identify by using temps. Within for a system of electron spins in a lattice, a temperature such that the population of the energy levels of the spin system is distributed by the Boltzmann distributionwith the spin temp. To accomplish thermodynamic equilibrium various nuclear spins must socialize among themselves. This took place scheduled to nuclear spin-spin magnetic discussion.

Subatomic particles like electrons, protons and neutrons can be imagined as spinning on the axes. In lots of atoms these spins are paired against each other, in a way that the nucleus of the atom does not have any overall spin. In some atoms the nucleus shows overall spin. The guidelines for determining the web spin of a nucleus receive below;

- If the number of neutrons
**and**the range of protons are both even, then the nucleus has**NO**spin. (Classical Particles) - If the amount of neutrons
**plus**the amount of protons is unusual, then the nucleus has a half-integer spin (i. e. 1/2, 3/2, 5/2) (Fermions) - If the number of neutrons
**and**the variety of protons are both strange, then your nucleus comes with an integer spin (i. e. 1, 2, 3) (Boson)

It is described in Quantum technicians a nucleus of spinIwill have 2I+ 1 possible orientations. A nucleus with spin 1/2 will have 2 possible orientations. Inside the absence of an exterior magnetic field, these orientations are of equal energy. If the magnetic field is applied, then your energy levels divide. If the nucleus is at a magnetic field, the original populations of the energy levels are dependant on thermodynamics, as described by the Boltzmann distribution. It means that"the lower vitality will contain just a bit more nuclei than the bigger level". It is possible to excite these nuclei in to the higher level with electromagnetic radiation. The occurrence of radiation needed is determined by the difference in energy between your energy levels.

This spin-spin process can be characterized by using rest process. Nuclei in the bigger energy state return to the lower point out by emitting rays. At radio frequencies, re-emission is negligible. You will find two main leisure processes;

- Spin - lattice (longitudinal) relaxation
- Spin - spin (transverse) relaxation

Spin - lattice rest (T1)

Nuclei that are in a sample create a complex magnetic field. The magnetic field brought on by action of nuclei within the lattice is called thelattice field. This lattice field has many components. A few of these components will be identical in regularity and phase to the Larmor occurrence of the nuclei of interest. These components of the lattice field can interact with nuclei in the higher energy talk about and lead them to lose energy time for the lower status. The energy that a nucleus loses increases the amount of vibration and rotation within the lattice resulting in a tiny rise in the temps of the sample.

The rest time, T1(the common lifetime of nuclei in the bigger energy status) would depend on the magnetogyric percentage of the nucleus and the mobility of the lattice. As flexibility rises, the vibrational and rotational frequencies increase, rendering it much more likely for a component of the lattice field to have the ability to interact with excited nuclei. However, at extremely high mobilities, the likelihood of a component of the lattice field having the ability to interact with fired up nuclei lowers.

Spin - spin rest (T2)

This is describing the conversation between neighbouring nuclei with equivalent precessional frequencies but differing magnetic quantum claims. In this case, the nuclei can exchange quantum states; a nucleus in the lower vitality will be excited, while the thrilled nucleus relaxes to the low energy state. There is nonetchange in the populations of the states, but the average lifetime of a nucleus in the ecstatic state will decrease. This can cause line-broadening.

Most of the nuclear systems don't meet the conditions in negative conditions.

By taking a look at each one of these things we can conclude that even though the phenomena of negative heat range is a fully valid idea in thermodynamics and statistical technicians they may have less important than phenomena of positive temps.

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