Recent content by clint

1. Phase change hysteresis

Turin, hope this helps , clint Say one chooses to do an experiment across a liquid/solid phase transition, with constant pressure consitions. One starts with the material in its high temperature liquid state which is sealed inside a closed high pressure cylinder with a piston at one end (or...
2. Entropy of photons

The total energy of our universe is constant, yet entropy certainly plays a role. As remarked, it doesn't make sense to discuss the entropy of a "single" photon. Entropy S applies to large numbers (distributions) of photons, like in Stephan-Boltzmann theory of radiation from an object (star...
3. Entropy of photons

Try Mr. Tomkins in Paperback by G. Gamow. .. he postulates the universe if c was smaller and h-bar larger. Thinking about extremes does help somewhat, but we can only ever really accelerate at g before feeling rough!!
4. Nuclear magnetic resonance

I wasn't so sure where your discussion was going; hope this helps. In nmr, the ensemble of nuclei is subject to a constant magnetic field Ho (~10 Tesla), which in the case above is taken along the +z direction. The perturbation is a radio frequency (rf) magnetic field H1 (~10 Gauss) at the...
5. Phase change hysteresis

Taking H2O from solid to liquid at a fixed pressure takes heat, its Latent heat. Say you have a block of ice at -10C and at 1 atmosphere of pressure. You then hook up a heater to the block, and keeping the pressure constant, then you turn on the heater at a moderate but constant heating rate...
6. Electrons & Braggs Law

Right, the Bragg law is 2*d_hkl*sin(theta) = n*Lamda I was using the what you wrote without the factor 2. Still, as long as the energy isn't in the vicinty of Ef, free electron model is fine I think.
7. Cooper Pairing

" Fermi surfaces are used in superconductor theory.An electron that has a higher energy than the minimum can move onto a fermi surface. Do cooper pairs move onto fermi surfaces or only unpaired conduction electrons?" Three necessary ingredients to Cooper paring are; a well defined Fermi...
8. Electrons & Braggs Law

Using a=0.361nm and theta=90 (i.e. normal incidence and 180 change in direction or back scattering) gives Lamda=a, and Bragg's law is satisfied for Ea=11.5eV (23eV) for i (ii). Try your numbers again, and see if you agree. So this is the opposite. Ea>Ef=7eV, which makes Cu free electron like...
9. Cooper Pairing

"What is the fundamental reason that pressure makes these holes appear?" Actually, not surprisingly, the situation is not as straight forward as I suggested. What I was refering to was the case of CuO2 ladder systems which have recently been found to superconduct under application of high...
10. Cooper Pairing

Pressure effects on Tc, and Cooper pair tunnelling With regards to external pressure effects on Tc. Well ,the application of external pressure (usually in the 10,000's of atmospheres) on high Tc materials is primarily believed to increase the hole concentration N in the CuO2 planes...
11. Attraction between positive charge and negative charge

The neutron by itself decays thanks to the weak force, the electron itself does not decay thanks to charge conservation, but ... a proton alone ?
12. Cooper Pairing

Not quite. In conventional superconductors, the electron-electron attraction is a result of the electron-phonon interaction (where a phonon is a quanta of a lattice/atomic vibration), right? According to conventional superconductor theory then, the onset temperature of superconductivity...
13. Cooper Pairing

entropy Entropy (or the sum of -p.lnp. over all probabilities p at a given temperature) is determined experimentally by first measuring the specific heat capacity (C), that is, the heat required to raise the temperature of a material a Delta amount (s.i. units of C are of the order 10^-23...