This package is in the form of an Excel workbook, containing the following interactive diagrams:
  • Singly-reflected rays, giving rise to a primary rainbow
  • Doubly-reflected rays, giving rise to a secondary rainbow
  • Parallel rays of red light, allowing you to investigate the (Descartes) angle at which the emerging beams are most concentrated. (Other colours produce similar beams at slightly different angles, which explains why every raindrop splits the sunlight into a spectrum.)

  • Two further worksheets provide data and formulae enabling you to use Excel's optimization tool Solver to derive the primary and secondary rainbow angles numerically. (They can also be derived analytically using calculus.)
The workbook will enable you to trace the paths of two typical rays of light (red and violet) as they are reflected and refracted within a droplet of rain. You can then experiment by adjusting the angle at which the incident ray of white light hits the raindrop.

Download now (33K).

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