When rain storm passes and sun shines again in the sky, we sometimes see a brightly colored arch against the dark background of departing clouds apposite to the sun. The rainbow is an optical phenomenon produced by reflection, refraction and dispersion of sunlight in tiny spherical raindrops on which it falls. It is, in fact, the spectrum of sunlight formed by raindrops suspended in the air. The colors of rainbow are similar to those which are obtained in the solar spectrum through glass prism. The rainbow is so called because it is formed in bow shape. There are two types of rainbow.
Primary Rainbow:
This is formed by two refractions, one internal refraction and dispersion. In this, Violet color is on lower edge but red color is on outer edge.
Secondary Rainbow:
This is formed by two refractions, two internal reflections and dispersion. In this type of rain bow red color is at bottom whereas violet color is on the outer edge. It may noted that secondary rainbow is fainter than the primary rainbow.
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