A 40-year-old optometry patient focuses on a 6.50cm -tall photograph at his near

Question

A 40-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)

Figure 1 of 1

Part A

What is the effective focal length of his eye when he focuses on the photo?

2.24

Correct

Part B

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

44.5

Correct

Part C

How tall is the image of the photo on his retina?

7.39

Correct

Part D

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

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

Part E

If he views the photograph from a distance of 2.40m , how tall is its image on his retina?

f =

2.24

  cm   A 40-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) Figure 1 of 1 Part A What is the effective focal length of his eye when he focuses on the photo? f = 2.24 cm Correct Part B What is the power of his eye in diopters when he focuses on the photo? D = 44.5 diopters Correct Part C How tall is the image of the photo on his retina? |h?| = 7.39 mm Correct Part D Is the image mentioned in part C erect or inverted? Real or virtual? Is the image mentioned in part C erect or inverted? Real or virtual? The image is erect and virtual. The image is inverted and real. The image is inverted and virtual. The image is erect and real. Part E If he views the photograph from a distance of 2.40m , how tall is its image on his retina? |h??| = mm

Explanation / Answer

PART A) 1/obj dist + 1/image dist = 1/f

1/f = 1/22 + 1/2.50

f = 2.24 cm

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PART B) power in diopters is 1/f

power = 1 / 0.0224 = 44.5

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PART C) magnification = - 2.5 / 22 = -0.11

height of the image = 6.5 cm x 0.11 = 0.74 cm

= 7.4 mm

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PART E) 2.40 m = 240 cm

m = - 2.5 / 240 = 0.0104

image = 0.0104 x 6.5cm

= 0.068 cm = 0.68 mm

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