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Re: Controversial Exam Questions (WAS: R = V/I ?)



But what does the graph that accompanies the problem look like?
Regards,
Jack

Adam was by constitution and proclivity a scientist; I was the same, and
we loved to call ourselves by that great name...Our first memorable
scientific discovery was the law that water and like fluids run downhill,
not up.
Mark Twain, <Extract from Eve's Autobiography>

On Wed, 10 May 2000, Doug Craigen wrote:

Leigh Palmer wrote:

mark they had to "State whether or not the filament of the lamp obeys Ohm's
law"!

Ive tutored a lot students - and IB has been a large fraction. One
constant frustration is old exams or practice questions that they want
to go over which have more than one "right" answer in multiple choice
form. When its their own teacher's old exam I explain the debate and
tell them to ask their teacher which way (s)he is intending it, but when
its a widely distributed exam like IB I have to tell them to flip a coin
and hope for the best.

I hope you aren't suggesting that this question is ill posed. From what
you've been writing it is clear that you think the correct answer is
that the filament does not obey Ohm's law. Asked in that way it would
be impossible to reasonably argue otherwise.

This is a pet peeve, so I was inspired to spout from something rather
mild. I think most reasonable people looking at this wording would
agree that the answer is it doesn't obey Ohm's law, and the whole
context of the question may make it plainer still. However I could
easily come up with several lines of argument to the contrary if I
chose. For example, I could argue that it does obey Ohms law for a
certain range of voltages, and this in this it is no different than any
other "resistor". I'm guessing here, but would expect a 100 W bulb to
obey Ohm's law up to 5 V (at least), and this is a greater range than a
1 ohm "resistor" rated for 5 W of power. Even though I make this
argument purely for the sake of being argumentative, in a large enough
class I wouldn't be surprised to have a student come up with that sort
of interpretation. In fact I would go as far as to say it is often the
brightest students who find an unintended alternative view to what was
supposed to be an easy question.

If I find the time I'll dig for some better example of an actual exam
question which would actually would split the Physics community to a
reasonable extent.

()-()-()-()-()-()-()-()-()-()-()-()-()-()-()-()

Doug Craigen
http://www.dctech.com/physics/