What color does a red rose appear when green light is incident upon it?

$A$ 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 the figure. In which of the following cases,after dispersion,the third colour from the top corresponds to the colour of the sky?

What is the complementary color of red?

$A$ child sitting in a classroom is not able to read clearly the writing on the blackboard.
$(a)$ Name the type of defect from which his eye is suffering.
$(b)$ With the help of a ray diagram show how this defect can be remedied.

Why does it take some time to see objects in a cinema hall when we just enter the hall from bright sunlight? Explain in brief.

What is meant by the least distance of distinct vision? How does this vary between the very young and old people?