A rainbow is one of the most spectacular natural light shows observed in the sky. A number of
scientist and mathematician including Aristotle, Bacon, Theodoric, Descartes, Newton, Young,
Airy and Mie have worked on the explanation of various observations on rainbows. To
understand the formation of rainbow one should actually study the refraction, internal reflection
dispersion and total deviation of white light by the spherical water drop. A rainbow is produced
when sunlight falls and gets diverted to the eyes of the observer due to a large number of water
droplets in the sky on a rainy day. In addition to primary Rainbow there is a secondary rainbow.
It occurs in the same manner as the primary rainbow but due to two internal reflections. In
nature we can observe only primary and secondary rainbows. Higher order rainbows are never
seen since they are weaker than (i) the background sky brightness (i) the light reflected from the
outside surface of the drops and (ii) the light transmitted through the process with no internal
reflections.
a) What is refraction?
b) List two essential conditions for observing a rainbow.
c) What is the shape of a rainbow?
d) Why the red appears on the top of rainbow?
e) How is reflection different from total internal reflection?
Answers
Answer:
a) the fact or phenomenon of light, radio waves, etc. being deflected in passing obliquely through the interface between one medium and another or through a medium of varying density.
- change in direction of propagation of any wave as a result of its traveling at different speeds at different points along the wave front.
- measurement of the focusing characteristics of an eye or eyes.
b) Conditions necessary to observe a rainbow: (1) The Sun should be behind us. (2) It should have rained and the Sun should be present.
c) Rainbows are actually full circles. The antisolar point is the center of the circle. Viewers in aircraft can sometimes see these circular rainbows. Viewers on the ground can only see the light reflected by raindrops above the horizon.
d) The violet light (the lowest wavelength seen by eye) is deviated the most from the direction of incidence, the red light (the greatest wavelength) is deviated the least. ... Thus, a rainbow is red on top and violet on the bottom.
e) During normal reflection, only a portion of the total energy in the light is reflected. Parts of it are scattered, while others are refracted. In total internal reflection, the light intensity is higher, and the objects shine brighter than in ordinary reflection. Due to total internal reflection, diamonds sparkle.
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Explanation:
the answers are given below
