FORMATION OF RAINBOW
WHAT IS RAINBOW?
 An arch of colors formed in the sky in certain circumstances,
caused by the refraction and dispersion of the sun's light by rain or
other water droplets in the atmosphere
HOW IS RAINBOW FORMED?
 Rainbow is formed when White light separates into
different colours on entering the raindrop due
to dispersion, causing red light to be refracted less than
blue light.
 The formation of a rainbow involves reflection,
refraction, dispersion and total internal reflection.
BASIC 7 STEPS OF HOW
RAINBOW IS FORMED:
1. Light from sun strikes raindrop.
2. Some of the light is reflected. (Reflection)
3. The rest of the light is refracted. (Refraction)
4. White light splits into component colours. (Dispersion)
5. Light is reflected at rear of raindrop. (Reflection)
6. Light is refracted again as it leaves raindrop. (Refraction)
7. Colours are further dispersed (Dispersion)
VIDEOS ON HOW
RAINBOWS ARE FORMED
 http://www.youtube.com/watch?v=r_hFjFM91C4
 http://www.youtube.com/watch?v=AZsuZL89Tcs&feature=relat
ed
INTRODUCTION TO LIGHT
DISPERSION
 is the phenomenon where the colours of the white light separates
when different wavelengths of the different spectrum of colours of
the White light travel at different speeds and when they encounter a
change to medium that is more dense or less dense, the speeds are
effected by different amounts
REFLECTION OF LIGHT IN
WATER DROPLET
 At the rear of the raindrop, the light hits the water-to-air interface.
If the angle of incidence is greater than the critical angle, Total
Internal Reflection will occur and thus causing rainbow to be seen
REFRACTION OF LIGHT IN
WATER DROPLET
 Refraction happens when the light changed speed again as it leaves.
Here, the light is moving from a denser medium (water) to a less
dense medium (air). As it does so, it speeds up and its path bends. In
this case the path of the light rays bends away from the normal line
MAXIMUM ANGLE AT
WHICH LIGHT SHOULD
LEAVE DROPLET TO SEE
THE RAINBOW
 Primary rainbow and is produced by one internal reflection; the
secondary rainbow arises from two internal reflections and the rays
exit the drop at an angle of 50 degrees° for the secondary rainbow
and the rays exit the drop at an angle of 42 degrees° for the primary
rainbow
RAINBOW AS A 3D CONE
 Every raindrop 42° of the antisolar line is reflecting red light back
to our eyes. If we look at every raindrop that is 42° from this line, we
would see a circle of raindrops with the centre on the line. Raindrops
that contribute to your rainbow all lay on a cone with its apex at your
eye. So when you are looking at a rainbow, you are looking at the
collected light from many raindrops which, for a fleeting moment,
collectively produce a 3D cone with its apex at your eye