Timo A. Nieminen ha scritto:
On Fri, 22 Sep 2006, Sery wrote:
Timo A. Nieminen ha scritto:
On Thu, 21 Sep 2006, Sery wrote:
What is the reason for the Drude-Lorentz's model stops of valid being
for intense electric fields?
It assumes linearity and local response, and both will fail for
sufficiently high fields.
Exercise: think about what dielectric susceptibility means. Explain why
all real materials cannot have a constant susceptibility, given a
sufficiently high field.
Excuse me sir, but I do not know nothing about dielectrics.
Take some dielectric, put it in an electric field E. You get a
displacement field
D = epsilon_0 E + P
where P is the dipole moment per unit volume. Why do you get an induced
dipole moment? Because the electrons have some mobility, and the applied
field pushes them to one side.
The usual assumption for small fields is that P is proportional to E, so
we write P = z E, where z is some constant. But! There is a maximum
possible P, namely when all the electrons are on one side, and all of the
nuclei are on the other. Then P _cannot_ increase. Linearity must fail,
and likely fails long, long before that ultimate limits.
What similar ultimate limits might apply to the Drude model?
Dear Timo, My examinaton do not have in its interior dielectrics, so I
do not understand
when you write
D = epsilon_0 E + P
where P is the dipole moment per unit volume. Why do you get an induced
dipole moment? Because the electrons have some mobility, and the applied
field pushes them to one side.
The usual assumption for small fields is that P is proportional to E, so
we write P = z E, where z is some constant. But! There is a maximum
possible P, namely when all the electrons are on one side, and all of the
nuclei are on the other. Then P _cannot_ increase. Linearity must fail,
and likely fails long, long before that ultimate limits.
Thank you, Sere
--
Timo Nieminen - Home page: http://www.physics.uq.edu.au/people/nieminen/
E-prints: http://eprint.uq.edu.au/view/person/Nieminen,_Timo_A..html
Shrine to Spirits: http://www.users.bigpond.com/timo_nieminen/spirits.html
.
