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Spelling and Grammar in our e-mails



I really appreciated learning about Mark Sylvester's experience
using a hologen lamp as a source in a polarization experiment.
While reading his interesting comments, the verb, "learnt"
that he used happened to catch my eye. In my younger days,
I did a considerable amount of professional proofreading
as a technical writer. I remembered that back in school, we were
always cautioned to say "learned" rather than the incorrect
word "learnt"

However, I just checked my Webster's Dictionary and, sure enough,
the word "learnt" was listed there along with some other
accepted choices. I was wondering if anyone else on this
list-serve had similar experiences. ...... These days
the youngsters seem to be taking even wider liberties
in their use of their English grammar. Have you ever
seen their e-mails to each other?

Herb Gottlieb from New York City
Where only our New York Times newspaper seemd to be paying
attention to our old-fashioned spelling and grammar)



On Sat, 08 Mar 2003 01:26:26 +0100 Mark Sylvester <msylvest@XNET.IT>
writes:
The variation is certainly noticeable when one uses the Pasco "light
sensor" with a datalogging interface. We were using a halogen lamp
on 12V
ac as the source in a polarisation experiment some time back. The
measurements drifted up and down in a regular way that turned out to
be a
slow beat between the 100 Hz of the mains and the sampling
frequency, not
quite 20 Hz. We learnt that we had to use well-smoothed DC. We also
learnt,
btw, that halogen lamps die very quickly when run at below their
rated voltage.

Mark

At 14:28 07/03/03 -0800, Bernard Cleyet wrote:
"There is some hysteresis caused by the time lag of the
temperature
response to
the heating/cooling cycles, but the difference in resistance due to
these
temperature excursions isn't a great fraction of the overall
average
resistance
as a function of time."

A 71/2 W lamp works well as a strobe for setting the speed of a
disk
turntable. Knowing this prompted me to check in my favo. reference
book,
Levi's Applied Optics. Sure nuff, lotsa data.

It gives heating ( brightness 0=>90% and cooling 100=>10%) times
and total
variation in brightness for various lamps powered by 50 and 60 Hz.

They also have extensive tables on W props from which one may
determine the
temperature and resistance. More easily, one (bc hopes to do) may
use a dual
beam (dual trace) o'scope directly. Or more hi-tech, digitize and
plot the
product.

Here's some, 115V 60 Hz, extracted data:

gas filled first:

W M*% t(h) (msec) t(c) (M* % variation
from mean,
total;
40 27 65 26
100 13 125 59
500 4.5 380 190

vacuum
6W 74! 39 12
40 14 128 58

Another, rather interesting, but conforms to intuition, is a graph
of
brightness variation (M*) with wavelength for a 120 V lamp (wattage
not given
-- is this like voltage?). The variation is 10% to 4%, 0.4 micron
to 1.2
(respectively)

The large values of t(h) and t(c) paradoxically belie the large
values of M*.
The paradox is resolved by examining the graphs of heating and
cooling. The
curves are approximately exponential, so, for example, a 40 W (gas
filled)
lamp's brightness (lumens) drops from 100% to less than 35% in only
ten
milliseconds. the eye's is a log detector, so not so obvious.
Despite W lamp
resistance is ~ linear WRT the applied voltage (quasi DC), I
suspect its
variation should be quite noticeable.

bc



David Bowman wrote:

Regarding Mark's observation:

Interesting to see the evolution of consensus on this topic. In
its
previous incarnation (inverbation?) on this list (when I
brought it
up) the
view was that the filament lamp is a non-ohmic *device* even if
the
tungsten wire is an ohmic conductor.

Mark

I suspect that this phenomenon may be a function of the set of
just
which list members happened to respond in these two cases.
Maybe
last time more of the non-ohmites answered the call, and this
time
the ohm-ites responded.

The thing is that an incandescent lamp plugged in to the local
electric utility will behave, to a pretty decent approximation,
'ohmically' because the filament doesn't change its absolute
temperature by a very great fraction over the time between
heating &
cooling cycles (1/100 sec in Europe & 1/120 sec in North
America) of
the applied AC waveform. To a semi-decent approximation, when
the
lamp is operating the instantaneous voltage and current wave
forms
obey V(t) = R*I(t) throughout all phases of the applied AC wave
where R is almost time independent. There is some hysteresis
caused by the time lag of the temperature response to the
heating/
cooling cycles, but the difference in resistance due to these
temperature excursions isn't a great fraction of the overall
average
resistance as a function of time.

Of course if the lamp was operated with a much higher frequency
AC
power source, then even these tiny (so-called non-ohmic)
hysteretic
effects would vanish. We just must not operate the lamp at
*such* a
high frequency that the filament's inductive reactance becomes
a
significant fraction of its resistance (otherwise it would be
an
inductive load rather than a resistive one). But there is a
wide
range of frequencies where this is not a problem and still the
lamp acts fully "ohmically".

David Bowman

Mark Sylvester
UWCAd
Duino Trieste Italy