For staters: How does physics turn into applications?
As an example, consider semiconductor lasers. Surely this is
an application of modern physics; you wouldn't have semiconductors
_or_ lasers without modern physics. And surely this is an
important application; there is a multi-billion-dollar market
for diode lasers.
But a laser diode all by itself isn't very interesting. You
could pass one around in class, but it wouldn't generate much
excitement.
To understand this, you have to think about the food chain. It
runs something like this:
system
(CD player, CD writer, surveying instrument,
communications network, target designator,
surgical instrument, etc. etc.)
/ \
/ \
/ \
subsystem other subsystems
(laser diode)
/ | \
/ | \
/ | \
physics physics lots of other stuff
(lasers) (semiconductors)
When teaching physics it is a challenge to let the students see
physics as a real part of their world. This challenge is nontrivial
because in many cases physics is low on the food chain. The
physics is there, but it is hard to see.
<digression>
We might also say, the physics is valuable, but the value is hard
to reckon. (This makes contact with the previous thread about how
to pick a valuable project.)
You can't do laser surgery without a laser. But by the same token
you can't do laser surgery unless you know how to do surgery. Both
contributions are indispensible; it is not meaningful to ask which
is "more" indispensible.
This leads to a conundrum in microeconomics: How do you reckon
the value of the physics contribution, and how do you reckon
the value of the surgical-skill contribution? If you try the
standard approach, calculating the "marginal productivity" of each
contribution, either you find that each is worth 100% of whole
enterprise (so that they add up to 200%, which is absurd) or if
you are more careful you decide that the whole concept of
marginal productivity doesn't make sense, since it requires the
existence of certain derivatives that don't exist.
</digression>
So: I am slightly worried that a one-semester "applications of
physics" course in the physics department will paint a misleading
picture of how modern physics fits into the real world. You can't
build a laser diode in class, and you can't build a CD-writer in
class, and anything you can do in class will be somewhat atypical
of real-world applications of physics. I suspect that the real
"applications of physics" courses are being taught under other
names, in the engineering department, and the chemistry department,
and the med school, and ....