What color does the region appear when red,green,and blue light overlap?

Why does the sky appear dark to passengers flying at high altitudes?

What is meant by accommodation of the eye?

Which of the following are the primary colours of light?

What are the two colors of light called whose mixture produces white light?

$A$ person cannot see objects distinctly when placed beyond $2\, m$.
$(a)$ Identify the eye defect.
$(b)$ Give two reasons for this defect.
$(c)$ Calculate the power and nature of the lens he should be using to see the distant objects clearly.
$(d)$ Draw the ray diagrams for the defective and the corrected eye.