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How does an eye focus the objects lying at various distances?

An eye can focus the images of the distant objects as well as that of the nearby objects on its retina by changing the focal length of its lens. The focal length of the eye-lens is changed by the action of the ciliary muscles. The ciliary muscles can change the thickness of the eye-lens and hence its focal length changes the converging power of the eye-lens.

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13 Which phenomenon of vision is made use of in cinematography? Explain briefly how it is used. 14 How do we see colours? 16 When is a person said to have developed cataract in his eye? How is the vision of a person having cataract restored? 17 Where should an object be placed in front of a convex lens so as to use it as a simple microscope?