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Re: lightbulbs



John Denker wrote:

I have no idea why someone would write such a foolish experiment into a
textbook. Obviously they neither tried it nor even thought about it
very hard.

This is a continuing problem with texts for high school and below,
especially below. I would guess not so much at the college level
because most schools use their own lab texts.

We all know that even a well-conceived lab seldom works very well the
first time around. There are always unanticipated problems, or it
turns out that equipment that you used with no trouble when you
"pre-tested" it gives the students enormous difficulties, or any of a
dozen other problems. Labs that work, or give the desired insights to
the students are almost never spontaneous, but the result of
perfecting the procedures over time. We're not talking about projects
here, where the students have great latitude in the design and
carrying out of the experiment and have time to make reluctant
equipment work, and to retake data that they didn't get right the
first (or second) time. What is under discussion here are the short
labs that are supposed to be done in a class period or less. There
isn't time to deal with equipment that doesn't do what it is supposed
to, or instructions that make no sense. They are supposed to do a
simple, straightforward experiment with reliable, predictable results
and prepare a brief report on it all within a half-hour or so. No
undirected discovery here.

Well, the texts that are written for early HS and pre-HS classes are
almost never written by classroom teachers and the lab exercises that
they offer have almost never been done by students of the level the
experiments are intended for. I recall one text that has a whole list
of pressure-related experiments using large plastic syringes to
generate the pressure. The problem was that the pressures needed to
do these experiments were so great that the teachers could seldom
operate the apparatus (pressing the plunger while holding the
syringe), let alone the sixth graders who were supposed to do them.
In another experiment, the students were to build a cartesian diver
from another syringe, and read the liquid level in the syringe at
various points (at the top-positive buoyancy; in the middle-neutral
buoyancy; at the bottom-negative buoyancy). They had to do this on a
syringe where the three levels differed by about one or two scale
divisions, while the diver was inside the water-filled bottle. No one
was able to read the numbers. But then they had to make a graph that
tried to compare two unrelated parameters of the experiment--it was a
few years ago and I have mercifully forgotten exactly what they were
trying to do.

Anyway, the book was filled with these experiments that had obviously
been thought up by a committee and then never actually carried out. I
have looked over several other texts with similar results.

And it isn't just text writers that do these egregious things. I got
a lab computer interface as a demo some years ago, along with a book
of chemistry and physics experiments that were supposed to be doable
using the company's interface apparatus and their probes and
software. Again, it became obvious as another teacher and I tried to
do some of the experiments laid out in detail in their book, that
they had never been done by anyone. In one experiment using the pH
probe, all of the concentrations of the solutions that we were
supposed to use were specified several orders of magnitude too high.
Other experiments required measurements that simply could not be made
with the apparatus as we got it. this was to bad, since when used
within the design parameters, the apparatus worked beautifully, and
was easy to use. But had we bought it, we would not have been able to
use their lab book.

When we provide teachers with materials like this, we set them up for
failure. But the people who promulgate this garbage never get blamed.
It is always the poor teacher who is stuck with having to use
something that is basically unusable. I guess it wouldn't be too bad
if the teachers were better prepared so they could either modify the
instructions or create their own, but for the most part they just
don't have the depth of understanding of their subjects to be able to
do that, and they are heavily dependent on material prepared by
others. Not only have we let them down by not preparing them well, we
hammer them into the ground by then giving them unusable materials.
And we wonder why our schools are in trouble.

Hugh


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Hugh Haskell

<mailto://haskell@odie.ncssm.edu>
<mailto://hhaskell@mindspring.com>

The box said "Requires Windows 95 or better." So I bought a Macintosh.
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