The change in focal length of an eye lens is caused by the action of the

Why does the Sun appear reddish early in the morning?

Make a diagram to show how hypermetropia is corrected. The near point of a hypermetropic eye is $1 \, m$. What is the power of the lens required to correct this defect? Assume that the near point of the normal eye is $25 \, cm$.

Explain why the planets do not twinkle.

Why does the sky appear dark instead of blue to an astronaut?

The least distance of distinct vision for a young adult with normal vision is about ...... $cm$.