Which of the following is true for the eye defect known as hypermetropia (farsightedness)?

What is the iris?

Mention the factor on which scattering of light depends. Why does the sky appear dark in space?

$A$ person cannot see objects distinctly when placed at a distance less than $50\, cm$.
$(a)$ Identify the defect of vision.
$(b)$ Give two reasons for this defect.
$(c)$ Calculate the power and nature of the lens he should be using to see clearly the object placed at a distance of $25\, cm$ from his eyes.
$(d)$ Draw the ray diagrams for the defective and the corrected eye.

How will you use two identical prisms so that a narrow beam of white light incident on one prism emerges out of the second prism as white light? Draw the diagram.

Why is the colour of the sky blue?