A prism ABC (with BC as a 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 colour from the top corresponds to the colour of the sky? (a) (i) (b) (ii) (c) (iii) (d) (iv)

Answer: (b) (ii)

When the prism is reversed, the colours that are noticed after dispersion are: VIBGYOR. As a result, figure (ii) is the correct image to obtain the third colour, which is blue, as the colour of the sky.

  • Band of colour show violet at the bottom of the prism is kept with BC in the bottom.
  • If the prism is kept with BC at the top, then violet will be at the top followed by indigo and blue.

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