A person needs a lens of power – 5.5 diopters for correcting his distant vision. For correcting his near vision he needs a lens of power + 1.5 diopter. What is the focal length of the lens required for correcting i. distant vision, and ii. Near vision?

Study the given diagram and answer the questions that follows:

i. Which defect of vision is represented in this case? Give a reason for your answer.

ii. What could be the two causes of this defect?

iii. With the help of a diagram showing how this defect can be corrected by the use of the suitable lens.

Explain the structure and function of a human eye. How are we able to see nearby as well as distant objects?

Give reasons for each of the following:

i. The sky appears dark instead of blue to an astronaut in space.

ii. The sky near the horizon appears to have a reddish hue at the time of sunset and sunrise.

iii. The stars appear to twinkle.

Write the functions of each of the following parts of the human eye:

i. Cornea

ii. Iris

iii. Crystalline (Eye) lens

iv. Ciliary muscles

v. Retina