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

$A$ myopic person has been using spectacles of power $-1.00\, D$ for clear vision. During old age,he also needs to use separate reading glasses of power $+2.00\, D$. Explain what may have happened to his eyesight?

Why does it take some time to see objects in a dim room when we enter the room from bright sunlight outside?

What is another name for the defect of myopia?

$(a)$ Explain the following terms used in relation to defects of vision and corrections provided for them:
$(i)$ Myopia $(ii)$ Astigmatism $(iii)$ Bifocal lenses $(iv)$ Far-sightedness (Hypermetropia).
$(b)$ Describe with a ray diagram how a person with myopia can be helped by spectacles.

$A$ 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.