Phys 10, Gweon, Lecture of Nov 28

Student Name ____________________________________


1. (OPTIONAL)  Consider a free non-relativistic electron with momentum
p_1 and energy E_1.  What is the momentum-energy relationship?
Consider a photon with wave vector k and angular frequency w,
propagating in free space.  Its momentum and energy are given by p =
hbar * k, E = hbar * w, where hbar is the Planck constant divided by
2*pi.  What is the relationship between E and p?  Consider a process by
which the electron with p_1 and E_1 absorbs the photon with p and E.
Let's denote the final momentum of the electron as p_2 and the final
energy of the electron as E_2.  Show from the conservation principle of
momentum and energy that this photoelectric process just described is
not possible.  Consider a more realistic situation where the electron
is bound to a nucleus.  Is the photoelectric effect possible in this
case?  Note that above all momentum values must be considered as
vectors.

2.  Consider the following passage from Robert Laughlin's book, "A
different universe", p16.  [available for reading/searching in
www.amazon.com]

"[1] But there is another, equally important, truth that the
expressways and trains are always jammed with commuters at certain
times of day, ...

[2] It is certainly imaginable that all these commuters might get the
stomach flu on the same day and stay home, but it is so unlikely as to
be effectively impossible.

[1]' The commute condition is a simple, reliable phenomenon that
emerges out of complex decisions made by a large number of individuals
as they go about their lives.

[3] It is not necessary to know what various individuals had for
breakfast, where they work, what the numbers and names of their
children are, and so forth, in order to appreciate that it's hell out
there at 8:15 in the morning.

[1]" Commuting traffic, like the behavior of dilute gas, is a
collective certainty."

(Numbers [1], [2], [3] inserted by GHG.)

Provide your own example of a collective phenomenon in every day life
or in any physical systems, like [1].  In giving this example, explain
what the imaginable but practically impossible event may be, in analogy
with [2], and what type of individual variables are completely
unnecessary to know in order to explain the collective phenomenon, as
in [3].