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Re: funny capacitor (EXCEL)



I learned how to use Excel 97 to solve the Q(V) problems
(see below). At the end of iterations I have potentials
displayed in all cells (with respect to my rectangular enclosure).
What I would like to do, but do not know how, is use colors
to identify potentials, for example:

red when 100>V>=90
pink when 90>V>=80
orange for 80>V>=70 etc.

Can somebody describe how to do this? Here is the outline
of steps I used in Excel:

1) My "universe" consists of cells from A1 to Z26. Why not?

2) I begin by populating all cells with zeros.

3) The formula =(B1+B3+A1+A3)/4 is entered into cell B2

4) That formula (relative addressing is essential) is copied
to all cells of the B2:Y25 region.

5) I want my cells to be square. To accomplish this I declare
the width of each cell to be 3 and its height 22 (using the
ROW and COLUMN commands from the FORMAT menu).

6) I want to begin with manually controlled iterations. In
other words I do not want iterations to begin automatically
each time something is changed in the spreadsheet (default).
To accomplish this I click the radio button "manual" in the
dialog box of the PREFERENCES command. That command
is located in the TOOLS menu; its dialog box has several
TABS; on of them is CALCULATIONS. The "manual"
button is under that tab.

7) To allow iterations I must check the ITERATION box.
It is located below the "manual" button described above.
To stop after each iteration I declare the "Maximum
iterations" to be 1 (instead of the suggested 100). After
checking that all is working fine I can increase the
maximum number of iterations.

8) Let me continue preparing the spreadsheet. Steps 6
and 7 were necessary; without them I would be often
distracted by automatic recalculations of the spreadsheet.
Suppose I am interested in distribution of potentials
between two plates of unequal size, one at V=0 (left)
and one at V=99 (right).

9) To create the right plate I put 99 into each cell of the
Q7:Q18 range. These numbers replace the formulas which
were placed there in step 4 above.

10) To create the left plate I put 0 into each cell of the
F14:F16 range. These numbers also replace the formulas
which were placed there in step 4 above.

11) I press the command/= keys (on my Macintosh) and
the first manual iteration takes place. I press the same
combination of keys and observe the outcome of the
second iteration.

12) All looks good. So I go back to the dialog box (see
step 6 above) and change the "Maximum iterations" to
1000. I like manual starting and for that reason the manual
box remains checked. In some situations the "automatic"
options could be more desirable, I suppose.

13) How to impose colors according to what is displayed
in cells? That was my question.

THAT IS IT. PLEASE ADD MORE STEPS TO SHARE
WHAT YOU KNOW. PERSONALLY I DO NOT LIKE
EXCEL BUT IT AVAILABLE EVERYWHERE AND
FOR THAT REASON IT IS A GOOD IDEA TO USE
IT IN TEACHING.
Ludwik Kowalski