You can click the "real intensity" checkbox to find out the relative intensity for different paths.
You can drag the black square near the left side of the simulation to drag those rays up and down.
You might notice that intensity for incoming rays are not the same. It is indicated that the cross section are not the same for different ray.
If the ray is off by the center of the water drop by distance b, and the rasius of the circle is R.
The incident angle , where, the effective cross section is proportional to
If the index of refraction is n, the refracted angle, where.
If the intensity of incoming ray is , then the intensity for the reflected ray(s wave) is and the intensity for refracted light is '
The above formulas are used to calculate the intensity for different ray.
I hope the above simulation can help you understand more about the physics of rainbow.
[b]You are welcomed to check out [url=http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=44]Physics of Rainbow[/url] for more in depth discussion about rainbow[/b]