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

["Richard W. Tarara" <rtarara@SAINTMARYS.EDU>]

Wouldn't the 'R is defined as V/I' proponents have to say that any device
with a well defined V/I behavior follows Ohm's Law?  The resistance is
'defined' at each point on the curve and IS 'defined' by the use of Ohm's
Law.  The fact that the resistance changes shouldn't be a problem.

On the other hand if one prefers I = V/R with R a constant, then Ohm's Law
is not satisfied by a light bulb.

Rick

----- Original Message -----
From: "Doug Craigen" <dcc@ESCAPE.CA>
> 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/