Showing posts with label heat. Show all posts
Showing posts with label heat. Show all posts

PHYSICS DICTIONARY

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Hadrons

Kaons, Pions together with Baryons are placed in group of strongly interacting particles called Hadrons.


Half Life

Term used in nuclear physics. It represents the time it takes for a radioactive isotope for decaying its activity to half of its present value.


Half Wave Plate

Plate of uniaxial double refracting crystals such as quartz and calcite with optic axis parallel to their refracting surface, the thickness of which is such that it produces a path difference of Ν/2 or a phase difference Π in between ordinary and extra ordinary waves.


Half-Wave Rectifier

Device which conducts current only during the positive half cycles of input ac supply. The negative half cycles of ac supply are suppressed i.e. during negative half cycles, no current is conducted and hence no voltage appears across load. Therefore, current always flows in one direction (DC) through load after every half cycle. 


Hall Effect

When a piece of semiconductor carrying a current is placed in a transverse magnetic field, an electric field is produced inside the conductor in a direction normal to both current and magnetic field.


Hall Mobility

Mobility of charge carriers under Hall Effect defined as product of hall coefficient and conductivity.


Hall Probe

Hall probe is a magnetic field sensor that passes electric current when the sensor is perpendicular to magnetic field. The stranger the magnetic field the more the current is converted to voltage. They are used for proximity switching, positioning etc.


Hamilton’s Principle

If a particle moves from one point to other in time interval t1 t t2, then the actual path it follows is the one for which action assume stationary value.


Hamiltonian Principle

The path actually traversed by a conservative, holonomic dynamical system from time t1 to t2 is one over which the integral of the lagrangian between limits t1 and t2 is stationary i.e., the time integral of lagrangian is extremum.


Hard Radiation

The term attributed to high energetic X-rays or gamma rays having high penetration power into almost all materials. 


Hardness

Mechanical property which is a measure of materials resistance to localized plastic deformation.


Harmonic Motion

 See simple harmonic motion.


Health Physics

It is branch of physics which deals with radiation protection of occupational workers in nuclear reactors and other radiation material handling centers.

 

Heat Capacity

The quantity of heat required to raise the temperature of the whole body there 1oC or 1oK is called heat capacity of body.


Heat Engine Law

Conversion of total heat energy into work is impossible.


Heat Engine

It is cyclic process in which heat is continuously converted into mechanical work. It has 3 main parts: source, sink and working substance. i) Source of heat at constant temperature to drive heat; ii) Sink at constant temperature, heat can be supplied without change in temperature. iii) Working substance: absorbs heat from source, converts part of the heat into mechanical work & rejects remaining heat to sink.


Heat

It is a form of energy (kinetic energy of molecules constituting the body) which produces sensation of warmth.

                                      (or)

It is energy that is transferred between a system and its environment because of a temperature difference that exists between them.


Heavy Water

Also referred as Deuterium oxide, is a type of water in which Deuterium (an isotope of Hydrogen) substitutes Hydrogen i.e. D2O. It has importance for having properties like Neutron moderation, high boiling point etc.


Heisenberg Forces

Type of nuclear force in which there is exchange of both spin and position coordinates.


Heisenberg’s Uncertainty Principle

Based on wave nature of matter, Heisenberg proposed a principle according to which, macroscopically it is possible to exactly measure position of moving particle and momentum associated with it but microscopically it is not possible. According to this principle, product of uncertainties in the measurement of position and momentum is of order of h/2π; where ‘h’ is Planck’s constant.


Helicity

Lee and yang suggested that the violation of parity in beta decay was direct consequence of longitudinal polarization of emitted electrons and Neutrons. The state and degree of longitudinal polarization of particles is represented by the term Helicity.


Heliocentric Theory

The theory proposed by Nicolas Copernicus, a polish astronomer. Heliocentric system first appeared in his book “De revolutionibus orbium coelestium”, “on the revolutions of heavenly bodies” which appeared in 1543. “Helios” in Greek means “sun”. Heliocentric means that the sun is at the center. As per this theory, sun remains at center and all the planets revolve round it. The moon is only celestial sphere in the system that revolves round the earth and together around sun. 

What does First Law of Thermodynamics infer us?

  • It is impossible to derive any work without expenditure of an equivalent amount of energy in some other forms. 
  • Heat absorbed by the system should be taken positive. Heat rejected by the system should be taken negative. 
  • For an ideal gas the total kinetic energy (KE) of all its molecules is called internal energy(U). For such a gas the internal energy depends only on Temperature.

GIBBS CANONICAL ENSEMBLE

(SYSTEM IN CONTACT WITH A HEAT RESERVOIR)

Canonical ensemble describes those systems that are not isolated but are in contact with a heat reservoir.

The system under consideration together with a heat reservoir forms a closed system and then system of interest is taken as sub system of this closed system.

Any sub system of an isolated system in statistical equilibrium can be represented by a canonical ensemble.

The probability density of a canonical ensemble depends both on Energy 'E' and temperature 'T'

It is given by

ρ(E,T) = Ae-E/𝜏

Partition function for canonical ensemble

z=(1/h³âż.n!)∫exp(-E(q,p)/KTdΓ

The statistical energy of a system in a canonical ensemble is given by


𝜎 = logZ  +(E/𝜏);  𝜎 = logZ  +T[∂(log Z)/∂T]

Thermodynamical entropy 'S' of a system in a canonical ensemble is given by

S=K𝜎

S=KlogZ + (E/T); U=KT2[∂(log Z)/∂T]

The entropy at absolute zero in a canonical ensemble can be expressed as

 S=K.log gₒ

gₒ is statistical weight of ground state

Difference between Temperature and Heat

Heat is a form of (Thermal) energy due to the kinetic energy of molecules in a substance. Temperature is measure of hotness or coldness of a body. Temperature is a measurement of the average kinetic energy of the molecules in an object or system.

Mathematically, dQ = k dT; where dQ is the change in heat content, k is a constant of proportionality, and dT is the change in temperature (usually in degrees Kelvin).