Light rays entering the eye are refracted by the lens and form an image on a specific part of the eye. What is this part called?

Which part of the eye is responsible for changing the focal length of the eye lens by adjusting its thickness?

Why does the clear sky appear blue? How would the sky appear in the absence of Earth's atmosphere?

Draw a neat diagram to show the refraction of a light ray through a glass prism,and label on it the angle of incidence,and angle of deviation.

$A$ person cannot read a book at distances less than $50\, cm$. Name the defect of vision he is suffering from. How can it be corrected? Draw ray diagrams to show the image formation
$(i)$ by defective eye and
$(ii)$ after using corrective lens.

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