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Re: out-of-the-box thinking



On the other hand the value of the acceleration is positive assuming +
is to the right. When you ask if the answer is different for the value
of the acceleration if you assume a different direction of motion, many
students will say yes!!!!!

John M. Clement
Houston, TX

-----Original Message-----
From: Forum for Physics Educators [mailto:PHYS-L@lists.nau.edu] On
Behalf
Of Kossom
Sent: Wednesday, June 04, 2003 6:52 PM
To: PHYS-L@lists.nau.edu
Subject: Re: out-of-the-box thinking

Howdy-

From: John S. Denker
Sent: 6/4/03 4:39 PM

In your classes, do you set up situations where
out-of-the-box thinking is appropriate? Necessary?
Is it part of the routine procedure? Does it
get rewarded? Can you share some examples?


I am fond of including essay questions on my tests.

One of the questions I often ask during the acceleration section is

Below is a series of lines made by a machine that marks
the stripes on the street. If the machine always sprays the
paint
for the same length of time, is the machine speeding up, slowing
down,

maintaining a constant velocity or that can't be determined.
Defend
your answer.

--- --- --- --- --- --- --- --- ---

Most students say that the machine is speeding up, giving the usual
reasons.
This is a really easy question since we use tape timers in the lab.

Over the years, though, a few students have noticed two problems with
the
question. Do you see them?

Should I change the question, or isit good to let some students find
them
on their own? I give bonus points to students who find significant
alternative answers or flaws. I hope that this encourages students to
think
outside the box on tests, but it can also cause students to go down
blind
alleys on other tests.


* * *

For a bonus on the final I usually have this optics question.

In front of you is a soap dispenser. Ignore the orange soap at the
bottom; it is
not part of this question. Instead look at the two layers of
liquid
at
the top. The
top one is clear and the bottom one is blue. Which has a higher
index
of
refraction?

Since you can't see it., I'll tell you that the soap dispenser is a
cylinder. The students get to actually play with it.

Most of the students say that the blue liquid is one with the higher
refractive index because it is denser. Unfortunately, the clear liquid
is
the one with the higher index.

I expect them to discover this by noticing that the when looking down
through the clear to the blue, there is significant total internal
reflection, but none the other direction. The vast majority who get
the
question right do this.

However, several use the dispenser as a cylindrical lens and notice
that
the
clear part magnifies more than the blue part.

I'm fine with either answer, obviously.


Marc "Zeke" Kossover