A prism ABC (with BC as base) is placed in different orientations. A narrow beam of white light is incident on the prism as shown in figure. In which of the following cases, after dispersion, the third color from the top corresponds to the color of the sky?

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Solution

The correct option is B
When the white light passes through some transparent material such as glass prism, it splits into its seven constituent colors(VIBGYOR). This phenomenon of splitting of white light is known as dispersion of light.
We know that colour of sky is blue. So the third color from the top corresponds should be blue.
When light passes through prism, it spits and comes toward the base(BC) as shown.

Here, third colour from bottom is blue but we need blue colour from top. This can be achieved by flipping a prism by $180^{0}$ .
As shown below:

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