                   The Physics of Rainbows
                   =======================

The attached Excel workbook (RAINBOW.XLS) contains three interactive worksheets depicting the refraction & reflection of rays of light within a raindrop, as follows:

1. Primary rainbow (single reflection)

2. Secondary rainbow (double reflection)

3. Rainbow angle (at which the emerging beams are most concentrated).


Corresponding to each of these there is a further worksheet containing the underlying data & formulae.  

There are also two Optimization worksheets in which you can use the Excel Add-in Solver to determine the maximum & minimum deflection angles, which give rise to the Primary and Secondary rainbows respectively.  You can then compare these numerical optima with the angles you obtain graphically.


How to use the worksheets
=========================

First click on View/Full screen (and, if you like, switch off the row and column headers in the Options menu).  These steps will reduce the amount of distracting "screen furniture".

Use the vertical scrollbars on the left of the screen to experiment with different angles of incoming light, in accordance with the suggestions on each worksheet.

For the optimization worksheets you may first need to attach the Solver Add-in.


I hope you find this demonstration instructive.  Please let me know of any problems or suggestions for improvement at:

     ngreenwood@iname.com



Nigel Greenwood

March 2000