Re: Test Writing

[Herbert H Gottlieb <herbgottlieb@JUNO.COM>]

 

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)