What theory did Drude use for his model?
Kinetic theory of Gas
What is the kinetic theory of gas?
Molecules are treated as similar spheres that move in a line unless a force is acted upon them or they collide with one another.
What is the atomic structure of Drude’s theory?
Drude’s theory is based on the idea that metal is neutral: its atmic structre is made of valence electrons and metallic ions. The first are negative the second are positive.
What assumptions is Drude theory based on?
Neglection of interatcion
Insanteneous collisions
Probability 1/tao
thermal equilibrium
What is drift velocity and how can it be claculated?
Drift velocity is the velocity the electron obtains if a force is acted upon it. It is obtained by Newton’s law. If we let time act infinitly, velocity is infinte too thus we introduce the relaxation time.
What is thermal velocity?
The thermal velocity is the vleocity that all electrons have following from the thermal equilibrium.
What does damping parameter mean? Why do we introduce it?
A damping parameter is introduced in drude’s thoery to justify a not infinite current.
What is the order of magnitude we expect of a mean free path?
1nm
What problems did Drude model have?
The temperature dependance of conductvity is not experimentally observed.
At low relaxion time the mean free path is way bigger than 1nm.
How can we caluclate the change in momentum upon an external force applied?
Taylor series expansion
What is the hall coefficient?
The Hall coefficient unveils the nature of the charge carriers in conductors.
Why is Hall effect useful?
The hall effect can be used to measure the oncetnration of conduction electron.
Hwy is the curretn density in the y-direction zero?
The current between 2 electode in the hall effect is neglegible thus curet density is zero.
What is W_cT(omega_cTao)
it is a dimensionless meausre of the strengh of a magnetic field.
Why the conductivitiy of a metal goes to zero if the frequency of the applied current goes to high values,
The elctric fiels is changing from positive to negative much quicker than the electron can move between two collisions (1/tao)
What do we mean by local approximation?
The electric fiels is well defined at different location in the sample thus the wavelength of the field is large comapred to the mean free path.
What happened if we don’t have a local apporximation?
The math would include an integral which is annoying.
No local meas mean fre epath very long. Thus we have a ballisti equation.
What is plasma frequency?
The plasma frequency is the frequency at which the electrons in the plasma naturally oscillate relative to the ions
What happens when the frequency of the wave is smaller or larger than the plasma frequency?
If the plasma frequency is higher than no propagatio otherwise yes
What is a phonon?
It is a mode where there is heat even without conduction carriers
How is the temperature in the sample?
Linear
How is the thermal current defined as?
Density of particle x velocity x thermal energy
What is the meaning of the thermopower?
We have a metal, we introduce a temperature gradient, and we measure a voltage difference which is the same as electric field betwen 2 points in the direction of the gradient.
