Question

What change is made in the eye to enable it to focus on objects situated at different distances? Illustrate your answer with the help of diagrams.  

Answer 1

 

a) When the eye is focussed on a nearby object, the ciliary muscles of the eye contract, loosening the suspensory ligaments attached to the eye. As the ligaments become loose, they stop pulling the eye lens, because of which the eye lens bulges (or becomes more convex), increasing its converging power. As the converging power increases, the eye lens  converges the diverging rays of light from the nearby object to form its image on the retina.

(b) When the eye is focussed on a distant object, the ciliary muscles are completely relaxed. The relaxed ciliary muscles pull the suspensory ligaments tightly. As the ligaments become tight, they pull the eye lens, because of which the eye lens becomes thinner (or less convex). The focal length of the eye lens is the maximum but its converging power is the minimum. However, the small converging power is enough to converge the parallel light rays from the distant object and form its image on the retina.