On Sun, 21 Oct 2007 05:10:19 +0000 (UTC), (Dave
Martindale) wrote:

Mark Lloyd writes:

I was studying digital electronics in college, but did once take an
elective course in NEC. I remember getting one test question "wrong",
in one of those cases where you get penalized for knowing something
you aren't expected to.

The question was about a 3-phase wye-connected motor, and asked True
or False: the current in each leg is the same. The supposed "correct"
answer was True, although I knew that was impossible. One of things
they taught in electronics was that the sum of the currents in a node
is always zero (electrons are flowing FROM somewhere TO somewhere).
The currents could never be equal unless they were all zero.

They were asking about time-averaged current of some sort, probably RMS
current, while you were thinking in terms of instantaneous current.


At one particular time, you would see different voltages (and could
figure out the current would be different). You could not see phase
without seeing more than a singe instant.

That's sort of like being asked a question on a high school physics test
about the validity of Newton's laws when you already know about
relativity. *You* know that Newton's laws are not always valid, but at
the same time you should be able to figure out that *in the context of
the physics class*, they are.


There's many cases where honesty is NOT the best action. I often get
into trouble for that reason.

Dave
--
65 days until the winter solstice celebration

Mark Lloyd
http://notstupid.laughingsquid.com

"Unlike biological evolution. 'intelligent design' is
not a genuine scientific theory and, therefore, has
no place in the curriculum of our nation's public
school classes." -- Ted Kennedy