Re: Rainbow applet

[John Denker <jsd@MONMOUTH.COM>]

At 09:29 AM 9/25/99 -0500, Cliff Parker wrote:
> > If you look at the
> > "explanations" provided in high school textbooks you will see that
> > they aren't explanations at all. All they say is that light is
> > reflected and refracted within raindrops. Given such explanations a
> > student couldn't tell you whether red shows up on the outside or
> > the inside of a rainbow, and he wouldn't have a clue how to calculate
> > the angular size of the bow.
>
> You have me here.
> I must confess I do not fully understand the problem of the
> rainbow and I tell my students so, because you can be sure
> they will ask at some time during the year.

Check this out:  It is a java applet that demonstrates the correct physics
of a rainbow.
  http://www.phy.ntnu.edu.tw/java/Rainbow/rainbow.html

Note (!) that you can grab the incident ray with the mouse and drag it up
and down.  Watch how the 1-bounce emergent ray (#3) moves one way, pauses
at the *caustic* angle, and then moves back.  This is what produces the
primary bow at the caustic angle.  Ditto for the 2-bounce emergent ray
(#4), which produces the secondary bow at a slightly different angle.  Also
notice the little "3" and "4" markers sliding on the angle axis of the
intensity graph.


And BTW, on the page
  http://alboot.ba.infn.it/www/didattica.html
there is a pointer not only to the rainbow applet, but scads of other
things.  I haven't checked them all out, but if they are as cool as this
rainbow applet this is quite at trove.

______________________________________________________________
John S. Denker                                jsd@monmouth.com