Which part of the eye helps in changing the focal length of the eye lens to focus the image of objects lying at varying distances from the eye?

The peacock blue color is formed by the superposition of which two colors of light?

If the size of the scattering particles is large,which color of light do they scatter?

Through which part of the eye do light rays from an object first enter the eye?

What is Tyndall effect?

$A$ bifocal lens consists of both concave and convex lenses. Bifocal lenses are required by a person suffering from $.............$.
$P$ - Myopia (nearsightedness)
$Q$ - Hypermetropia (farsightedness)
$R$ - Presbyopia