Recent content by Cheetox

I'm wondering how one would go about measuring the conductivity of a semiconductor with variation in temperature, I assume the non ohmic behaviour prevents one from making simple voltage current measurements and then inferring resistance and the conductivity...any answers much appreciated...

Homework Statement Suggest how the energy difference arises between the optic and acoustic branches in a 1d diatomic chain.Homework Equations The Attempt at a Solution I know that on the optic branch atoms oscillate in anti-phase within the unit cell and in phase in the unit cell on the acoustic...

Ok so how do you then explain why holes are generally heavier?

Effect of Doping on Fermi Energy... I was wondering if anyone could give me a clear answer on why doping a semi conductor raises or lowers the fermi energy depending on n or p type semi conductors. There seem to be a few standard ways of explaining this, some to do with charge conservation or...

Homework Statement give a simple argument which will explain why holes in semiconductors are generally heavier and less mobile than electrons. Homework Equations The Attempt at a Solution Is it something to do with the fact that the hole represents the movements of a lot of...

I know that when a metal is compressed its fermi energy is increased. I would attempt to explain this by saying, "as the volume has been decreased, so has the allowed number of particle in a 3D box states, thus as we have the same number of electrons and fewer allowed states, and the pauli...

yeah I'm asking more about the validity of the free electron density of states model, cheers

Hi, In a lot of places it states that one of the great successes of the free electron model is that it gives, more or less, the metallic density of states, I understand that if you do the maths for a fermi gas you end up with a density of states = 3N/2Ef, but to what value do we compare this...

Yep am still on board and would love some solutions, cheers

Is the equation your referring to that could help us further the FRW equation? How would the effect of dark energy manifest itself in that?

Your not being confusing at all, very helpful indeed and yes I am aquatinted with the scale factor a(t).

I assume that it is an underestimate because the universe is not exactly matter dominated and thus t is greater than 2/3H0 (this is confusing as in a radiation dominated universe light only travels 2ct in the same time so I would expect th inclusion of the effects of radiation to reduce the...

Homework Statement Estimate the radius of the last scattering surface, using the age of the Universe. Why might this underestimate the true value? Homework Equations For a matter dominated universe particle horizon distance = 3ct The Attempt at a Solution I assumed the way to do...

Homework Statement At the time of decoupling the universe was 1/1000 of its present size. How for could light have traveled in the time up to decoupling? (assume that the universe was dominated by radiation until then) Homework Equations The Attempt at a Solution I'm a little...

Homework Statement Why can't we use perturbation theory to calculate the effect of the spin orbit interaction in hydrogen like uranium? Homework Equations The Attempt at a Solution Is it something to do with the fact that the perturbation must be small compared to the rest of the...