Re: Misconceptions assessments?

[Rondo JEFFERY <RJEFFERY@WEBER.EDU>]

Robert Cohen provided an interesting list of questions under this topic.  However, two or three of the answers he provided I would like to comment on.  Part of the problem, to be sure, is the difficulty in writing good multiple-choice answers, with no ambiguity.

> > > bbq@ESU.EDU 11/07/00 07:20AM >>>
> <snip>
> FWIW, I include some questions that I use to reveal common >misconceptions
> among my pre-service secondary science teachers.  I think part of the list
> was obtained from Indicators (some others I got from the Private Universe
> tapes).
>
> <snip>
> For each question, choose the best answer.
>
> Does the distance between the earth and sun stay the same all year
through?
> A.  Yes, within 1% or so.
> B.  No, the sun is much closer during the summer
> C.  No, the sun is much closer during the winter.
> D.  No, the sun is much closer during some other season.
> E.  No, the sun is much closer during various times during the year.

The answer given for this one is A.  However, this is poorly worded and misleading because of at least two things.  First, the difference between perihelion and aphelion distances is really 3-1/3 %.  This is far from what I would say would be a reasonable stretch of "1% or so".  Second point, what is the definition of "much", as in "much closer during winter"?  Is 3-1/3% "much", or would that have to be 20% or greater?  I answered A because I thought the writer of the question was looking for a small change, and would take "much closer" to be more that 3%.  But, that was a matter of guessing the intent of the writer (mind reading?).  A better wording would be "A. Yes, within a few percent..."  Then the other answers would give an indication of what "much closer" means, like 10% or more.

Another question:

> What is the main reason for it being colder in winter than in summer?
> A.  The earth is farther away from the sun in winter than in summer.
> B.  The hemisphere is farther away from the sun in winter than in summer.
> C.  The sunlight needs to go through more atmosphere in the winter.
> D.  The sunlight is spread over a greater area in winter.
> E.  More sunlight reflects off the earth in winter.
> F.  Other ________________________

  The answer given is D. I also picked this one, but thought C and E could have a good case made for them. And, in fact, none of the answers actually gives *the* "main" reason for the seasons.  The principal cause of the seasons is the tilt of the earth's axis in space.  Effects resulting from the tilt are things like answers C, D, and E, but also include fewer hours of daylight each day in winter.  So, any of these answers could be considered as *partially* correct.  (And students who pick them would argue strongly for them! :-)  )
  These secondary causes of the seasons are the ones most often cited, even in astronomy books, while the tilt of the axis may receive short schrift.  Other effects of lesser importance come from the shape of the orbit, and the fact that we are closer to the sun during northern hemisphere winter.  This also makes our (northerners') winters shorter and less severe than they otherwise would be.  This will change, of course, over the next 13,000 years due to precession, and we may not think of this as of lesser significance. ;-)

Rondo Jeffery
Weber State University
Ogden, UT 84408-2508

> <snip>
>
> ----------------------------------------------------------
> | Robert Cohen               Department of Physics       |
> |                            East Stroudsburg University |
> | bbq@esu.edu                East Stroudsburg, PA  18301 |
> | http://www.esu.edu/~bbq/   (570) 422-3428              |
> ----------------------------------------------------------