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Figure 34-47a shows the basic structure of a human eye.
Chapter , Problem 91(choose chapter or problem)
Figure 34-47a 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 (Fig. 34- 47b).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 (Fig. 34-47c). (a) Suppose that for the parallel rays of Figs. 34-47a and b, the focal length f of the effective thin lens of the eye is 2.50 cm. For an object at distance p ! 40.0 cm, what focal length f# of the effective lens is required for the object to be seen clearly? (b) Must the eye muscles increase or decrease the radii of curvature of the eye lens to give focal length f#?
Questions & Answers
QUESTION:
Figure 34-47a 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 (Fig. 34- 47b).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 (Fig. 34-47c). (a) Suppose that for the parallel rays of Figs. 34-47a and b, the focal length f of the effective thin lens of the eye is 2.50 cm. For an object at distance p ! 40.0 cm, what focal length f# of the effective lens is required for the object to be seen clearly? (b) Must the eye muscles increase or decrease the radii of curvature of the eye lens to give focal length f#?
ANSWER:Problem 91
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 (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 (Figure (c)).
(a) Suppose that for the parallel rays of figure (a) and (b), the focal length f of the effective thin lens of the eye is 2.50 cm. For an object at distance p = 40.0 cm, what focal length f’ of the effective lens is required for the object to be seen clearly?
(b) Must the eye muscles increase or decrease the radii of curvature of the eye lens to give focal length f’ ?
Step by Step Solution
Step 1 of 3
(a)
Consider as the new object distance and as the new focal length ,then
.
When the eye is relaxed,its lens focuses far-away objects on the retina,a distance behind the lens. We can set in the thin lens equation to obtain ,
where is the focal length of the relaxed effective lens. Thus , cm.
When the eye focuses on closer objects,the image distance remains the same but the object distance and focal length change.