Some aspects of Heat and Thermodynamics Or Thermal and Statistical Physics Prof. K. N. Joshipura Dept. of Physics Sardar Patel University Vallabh 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 by Syllabus/Curriculum/Course- examination etc………………!!!
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 examples Our 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 But Stefan’s law … ..???????..........
<ul><li>As Physics teachers we should have a historical background of the subject/topic. </li></ul><ul><li>It may not be a part of the syllabus but </li></ul><ul><li>A part of T-L process. </li></ul><ul><li>It works as an appetizer. </li></ul>
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….)
1773 James Watt, steam engine…. First step From Physics/science to technology 1824 Sadi Carnot, in Napoleon’s court Ideal heat engine …… .. beginning of the second law of thermodynamics….?!! 1845 James Prescot Joule Mechanical 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
1870s Ludwig Boltzmann, Log definition of entropy Moving Atoms as physical reality………….?!! 1870s James Clerk Maxwell Maxwell-Boltzmann distribution Statistical mechanics (electromagnetic theory….. …… Early dawn of modern physics)
Heat thermal concepts Temperature macro thinking Laws of thermodynamics Statistical Concepts What is there inside? Conceptual Developments Ideal gas model kinetic concept of Pressure
1eV ≡11,600°K E~ kT Temperature T °K Avg. kinetic energy Random motion E k – Boltzmann constant Micro to Macro link
Macro thinking / concept 2 nd law of thermodynamics Micro thinking, Statistical concept Micro state description Entropy, disorder Statistical mechanics, M-B statistics Efficiency Energy crisis, problem
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? Black-body Radiation
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 The UGC curriculum is now 10 years old….!!! UG Physics Initial conditions Inputs School /HSc boundary conditions UGC curriculum Outputs
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.