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

[Robert Cohen <Robert.Cohen@po-box.esu.edu>]

On Thursday, January 01, 2015 3:56 PM, John Denker wrote:

> I am a big fan of the building-block approach:  Given a complicated problem, you break it down in to small blocks,
> learn each block separately, and then put the blocks back together again, two at a time, three at a time, et cetera,
> until you have a finished edifice.

I agree.

Coming up with the simplest "block" is tricky though, as the widget rate puzzle illustrates.

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.

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