A 50-year-old optometry patient focuses on a 6.50cm -tall photograph at his near

Question

A 50-year-old optometry patient focuses on a 6.50cm -tall photograph at his near point. (See the table.) We can model his eye as a sphere 2.50cmin diameter, with a thin lens at the front and the retina at the rear.(Figure 1)

A. What is the effective focal length of his eye when he focuses on the photo? In centimeters

B. What is the power of his eye in diopters when he focuses on the photo? In diopters

C. How tall is the image of the photo on his retina? In millimeters

D.Is the image mentioned in part C erect or inverted? Real or virtual?

A 50-year-old optometry patient focuses on a 6.50cm -tall photograph at his near point. (See the table.) We can model his eye as a sphere 2.50cmin diameter, with a thin lens at the front and the retina at the rear.(Figure 1) A. What is the effective focal length of his eye when he focuses on the photo? In centimeters B. What is the power of his eye in diopters when he focuses on the photo? In diopters C. How tall is the image of the photo on his retina? In millimeters D.Is the image mentioned in part C erect or inverted? Real or virtual?

Explanation / Answer

a.) 1/u+1/i= 1/f     

       1/f = 1/22+1/2.50

        f=2.24 cm

b.)    power = 1/0.0224 = 44.6

c.) magnification = -i/u = - 2.5/22 = -0.11

     height= 6.5 cm x 0.11 = 0.74 cm = 7.4 mm

d.) Real and inverted

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