Q. Why does the sky appear dark instead of blue to astronauts ?

Q. The human eye can focus objects at different distances by adjusting the focal length of the eye.
This is due to:

1. Presbyopia
2. Accommodation
3. Far-sightedness
4. Near-sightedness

Q. A person needs a lens of power $-5.5$ dioptres for correcting his distance vision. For correcting his near vision he needs a lens of power $+1.5$ dioptre. What is the focal length of the lens required for correcting (i) distance vision, and (ii) near vision?

Q. Explain why the planets do not twinkle.

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

1. pupil
2. retina
3. iris
4. ciliary muscles

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

Q. A student has difficulty reading the blackboard while sitting in the last row. What could be the defect the child is suffering from? How can it be corrected?

Q. Write the values of the near point of the human eye with normal vision in cm.

Q. Why is a normal eye not able to see clearly the objects placed closer than 25 cm?

Q. Why do stars twinkle?

Q. The far point of a myopic person is $80cm$ in front of the eye. What is the nature and power of lens required to correct the problem?

Q. Why does the Sun appear reddish early in the morning?

Q. What is meant by power of accommodation of the eye?

Q. A person with a myopic eye cannot see objects beyond $1.2m$ distinctly. What should be the type of the corrective lens used to restore proper vision.

Q. What happens to the image distance in the eye when we increase the distance of an object from the eye ?

Q. The human eye forms the image of an object at its

1. cornea
2. iris
3. pupil
4. retina