How can a change in the size of the eyeball be a reason for $(a)$ Myopia and $(b)$ Hypermetropia? Compare the size of the eyeball with that of a normal eye in each case. How does this change in size affect the position of the image in each case?

$A$ glass slab is placed over a page on which the word $VIBGYOR$ is printed with each letter in its corresponding colour. $(i)$ Will the image of all the letters be in the same place? $(ii)$ If not, state which letter will be raised to the maximum. Give a reason for your answer.

$(a)$ What will be the colour of the sky in the absence of an atmosphere?
$(b)$ Why are traffic light signals (or danger signals) of red colour?

Cinematography makes use of

$A$ 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?

Name the delicate membrane in the eye having an enormous number of light-sensitive cells.