Figure (a) shows the basic structure of a human eye. Light refracts into the eye

Question

Figure (a) shows the basic structure of a human eye. Light refracts into the eye through the cornea and is then further redirected by a lens whose shape (and thus ability to focus the light) is controlled by muscles. We can treat the cornea and eye lens as a single effective thin lens as shown in figure (b). A "normal" eye can focus parallel light rays from a distant object O to a point on the retina at the back of the eye, where processing of the visual information begins. As an object is brought close to the eye, however, the muscles must change the shape of the lens so that rays form an inverted real image on the retina as in figure (c). Suppose that for the parallel rays of figure (a) and figure (b), the focal length f of the effective thin lens of the eye is 2.47 cm. For an object at distance p = 39.0 cm, what focal length f' of the effective lens is required for the object to be seen clearly? _____Cm Must the eye muscles increase or decrease the radii of curvature of the eye lens to give focal length f'? increase

Explanation / Answer

The eye focuses on objects at different distances by changing the focal length of the eye lens. This change is realized by changing its shape – decreasing its radius of curvature (and therefore shortening its focal length) as the object comes closer to the eye and increasing its radius of curvature (and therefore widening its focal length) as the object moves away to the eye.

Here, part (b) is asked which depends on the part (a) and hoped you must have found the f'.

So if f' > f , radius of curvature must be increased.

if f' < f, radius of curvature must be decreased.

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