Some aspects of

Heat and Thermodynamics

Or

Thermal and Statistical Physics

Prof. K. N. JoshipuraDept. of Physics

Sardar Patel UniversityVallabh Vidyanagar – 388120

KCG Orientation Programme, November 02, 2011

Let us look at the subject

by cutting across the party - lines drawn

by school/College/UG-PG

Or

bySyllabus/Curriculum/Course- examination

etc………………!!!

Pancha Mahabhutas

BY the way,

What is Fire/Flame?

Candle Flame, studied by Michael Faraday)

How do we start T-L of the topic?

light,

Sound

heat

Fundamental Sensations

Look at school/HSc levels

Notion of Heat, Temperature/Temperature

Scales

By day – to- day familiar examplesOur A/C ~ 24 .c Fever ~ 100 .F !

**********************************

Introduce Common terms like

Calorie (also food-calorie)

Sp. Heat / latent heat

Introduce ideas on

Thermal conduction,

Convention,

Radiation

Newton’s law of cooling

0( )dQ

T Tdt

4E TBut Stefan’s law

…..???????..........

As Physics teachers we should have a historical background of the subject/topic.

It may not be a part of the syllabus but

A part of T-L process.

It works as an appetizer.

1660 Robert Boyle………….. Boyle’s law, Beginning of the equation of state, almost in Newton’s time

1738 Daniel Bernoulli, Ideal Gas model Atomic collisons(Before the atomic concept of Dalton….)

1773James Watt, steam engine…. First step From Physics/science to technology

1824Sadi Carnot, in Napoleon’s courtIdeal heat engine …….. beginning of the second law of thermodynamics….?!!

1845 James Prescot JouleMechanical equivalent of Heat

1865 Rudolf Clausius Entropy, First and Second law

1850, First law of thermodynamics

1850-70, William Thomson, Lord Kelvin, A statement of the second law

1870sLudwig Boltzmann,Log definition of entropyMoving Atoms as physical reality………….?!!

1870sJames Clerk MaxwellMaxwell-Boltzmann distributionStatistical mechanics (electromagnetic theory…..……Early dawn of modern physics)

Heat thermal concepts

Heat thermal concepts

Temperature macro thinking

Temperature macro thinking

Laws of thermodynamics

Laws of thermodynamics

Statistical Concepts Statistical Concepts

What is there inside? What is there inside?

Conceptual Developments

Conceptual Developments

Ideal gas modelkinetic concept

ofPressure

Ideal gas modelkinetic concept

ofPressure

Temperature T °K

Avg. kinetic energyRandom motion E

k – Boltzmann constantMicro to Macro link

1eV ≡11,600°K

E~ kT

Macro thinking / concept

Macro thinking / concept

2nd law of thermodynamics

2nd law of thermodynamics

Micro thinking,Statistical concept

Micro thinking,Statistical concept

Micro state

description

Micro state

description

Entropy,disorder

Entropy,disorder

Statistical mechanics,

M-B statistics

Statistical mechanics,

M-B statistics

EfficiencyEfficiency

Energy crisis,

problem

Energy crisis,

problem

Black-body Radiation

Suppose that we have a Black – body……. perfect emitter/absorber Distribution depends on T only

BTW

Why is the Tungsten filament a black body?

Why is the Sun a black body?

The energy produced in the solar core by nuclear reactions is

initially in the kinetic energy of the charged reaction products

and some in the form of gamma rays of the order of MeV

energies. Tracking the energy release in the core to its

eventual release into space, to give the solar luminosity, the

energy released in the core is transported by radiation

through the radiative zone, by repeated scattering of high-

energy photons as they degrade in energy until they reach the

bottom of the convective zone ~10^6 years after the original

gamma ray left the core!

Is solar radiation BBR??

The radiative opacity of the solar material is an important

parameter. The energy at this point is transported to the

solar surface by the actual movement of hot gas that rises to

the surface, a physical process completely different from

energy transport by radiation. This process is convection, the

rise of hot gas to the photosphere through a hierarchy of

cells of different size so that the cooler gas above sinks and

there is a net flow of thermal energy to the solar surface.

All of the energetic photons from the core have been

absorbed by the time they reach the outer boundary of the

radiative zone, and the energy they carry is finally

transported convectively upward to the photosphere where

the gas density is too low to sustain convection. The

photospheric surface then radiates essentially as a blackbody

because it has been heated to an average temperature of

~5800 K.

A white light image of the full solar disk actually shows a

limb darkening. This is understood as a result of the rapid

fall in temperature with height, so that at the limb, the

cooler gas at a higher altitude radiates at lower intensity

than at disc center. There, the visible radiation comes

from a greater photospheric depth where the gas is

hotter and its radiant intensity is higher. According to this

picture, the lower level of the photosphere has a

temperature of ~6200 K, the upper level ~5400 K, and the

average disk temperature is ~5800 K.

Some T-L Issues

UG Physics UG Physics

Initial conditions

Inputs

School/HSc

boundary conditions

UGC curriculum

Outputs

The UGC curriculum is now 10 years old….!!!

If somehow all of scientific knowledge were to be destroyed, and only

one sentence passed on to the next generations of creatures, what

statement would contain the most information in the fewest words?

I believe it is the atomic hypothesis (or the atomic fact…. that all things are

made of atoms—little particles that move around in perpetual motion,

attracting

each other when they are a little distance apart, but repelling upon being

squeezed

into one another.

Thank

… …

…..You