Re: [Phys-L] widget rate puzzle ... reasoning, scaling, et cetera

["John Clement" <clement@hal-pc.org>]

A good ranking task might be just the ticket here.  Give them one where many
answers are the same, but a few are different.  There are now published
ranking tasks for E&M.

John M. Clement
Houston, TX 

> It is quite likely that students having problems with this 
> are too focused on the algebraic equation...Ohm's 
> Law...without much understanding of what the three quantities 
> in that equation actually are.
>
> I'd be careful to introduce and discuss current, resistance, 
> and voltage thoroughly before introducing Ohm's Law.  I will 
> have my classes come up with an equation for the resistance 
> of an object through analogy and 
> simple reasoning.   They will even come up with the idea of 
> temperature 
> dependency (which we then say we usually ignore!)  But at 
> this point, sans the temperature component, the resistance of 
> a given object (yes, between two specified points) is fixed 
> by its geometry and material.
>
> With that idea firmly in place, students may be less likely 
> to try and solve for the resistance as V/I and then be 
> befuddled because they don't know that the current is.
>
> To be honest though, I've never actually used the question 
> below in quizzing, so not sure how my groups would have fared.
>
> rwt
>
> > How about the following? Students frequently have trouble 
> with it. An 
> > ohmic resistor of resistance 10 ohms allows 1 A of current to flow 
> > when a voltage of 10 V is applied across it. What is the 
> resistance of 
> > the SAME resistor when a voltage of 100 V is applied across it? How 
> > would you help students who have difficulty with this 
> question? Philip 
> > Keller wrote:
> > > They are already functioning at the edge, not completely 
> convinced that thinking is a way to find things out.
> > When formulating your answer, keep PK's quote in mind.
> >
> > _______________________________________________
>
> --
> Richard Tarara
> Professor Emeritus
> Saint Mary's College
>
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> www.saintmarys.edu/~rtarara/software.html
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