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(a) A narrow beam of white light is inci...

(a) A narrow beam of white light is incident on three glass objects as shown below. Comment on the nature of the behaviour of the emergent beam in all three cases.

(b) There is a similarity between two of the emergent beams. Identify the two.

Text Solution

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(a) (1) The incident beam of light after refraction through the glass slab emerges parallel to the incident beam but is laterally shifted. No dispersion takes place in this case.
(2) The incident beam of light after refraction through the prism splits into a band of seven colours which are violet, indigo, blue, green, yellow, orange and red. These coloured rays emerge out of the prism along different directions and become distinct. Thus, in this case, dispersion of white light takes place.
(3) When the incident beam passes through the first prism, the prism splits it into a band of seven colours. These coloured rays are then incident on an identical inverted prism. Then the recombination of the coloured rays takes place. The emergent beam of light is parallel to the incident beam but slightly shifted outward.
(b) The emergent beam in the cases (1) and (3) are similar. In both the cases, the emergent beam is parallel to the incident beam and is laterally shifted.
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