Re: Test Writing

[Bernard Cleyet <anngeorg@PACBELL.NET>]

"1. You cannot always see a real image.   The real images that are formed
by a convex lens or a concave mirror are usually invisible. To see such an
image it is necessary to place a screen at the position that the image
forms .   If a screen is not placed at the image position ,  the image is

still formed  there .... but it is invisible."


Please give me a specific example (excluding those which cannot be seen
because ones head is in the way -- off axis and a diagonal mirror will? solve
that problem.) of an invisible real image.


"2. You can see a virtual image.  Just .........."

I think this is an analytic statement

bc


Herbert H Gottlieb wrote:

>

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> On Tue, 30 Apr 2002 07:53:03 -0500 Tina Fanetti
> <FanettT@QUEST.WITCC.CC.IA.US> writes:
> > I would prefer not to give multiple choice tests, however, there has
> > been some friction over the essay/short-answer questions.
> > Example:
> > On the last test I asked students to explain the difference between
> > a  real and a virtual image.
> >
> > Student answered:  You can see a real image.  You can't see a
> > virtual   image.  I took off points for this because it is not fully
> correct.
>
> ****************************************
>
> Perhaps Tina should have taken of more points for the student's
> answer because his answer was absolutely wrong for the following reasons:
>
> 1. You cannot always see a real image.   The real images that are formed
> by
> a convex lens or a concave mirror are usually invisible. To see such an
> image it is necessary to place a screen at the position that the image
> forms .   If a screen is not placed at the image position ,  the image is
>
> still formed  there .... but it is invisible.
>
> 2. You can see a virtual image.  Just look into a  plane mirror and there
> it is!
>
> Herb Gottlieb from New York City
> ( Where we can see virtual images but cannot always see real images)

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