Question

When ciliary muscles expand and contract,, what happens to the focal length of the eye lens?? Explain.

Answer 1

the image distance does not change in our eye.so for any object distance eye must form image on retina so accommodation of eye lens takes places

Answer 2

Eye lens of human eye is a convex lens. Being flexible, the eye lens can change its shape i.e. can become thin or thick to focus light on to the retina. The eye lens are held in position by the suspensory ligaments. One end of the suspensory ligaments is attached to the eye lens and the other end to the ciliary muscles . Ciliary muscles change the thickness of eye lens while focussing.When the eye is looking at a distant object, then the ciliary muscles  of the eye are fully relaxed and these relaxed ciliary mucles of the eye pull the suspensory ligaments attached to the eye lens tightly. The suspensory ligaments in turn pull the eye lens due to which the eye lens gets stretched and becomes thin .Thin eye lens has large focal length.Thus we can say that when the eye is relaxed, the interior lens becomes less rounded and the lens has its maximum focal length for viewing distant objects.