5. 5 points My Notes Presbyopia is the tendency to gradually become far-sighted

Question

5. 5 points My Notes Presbyopia is the tendency to gradually become far-sighted (hyperopic) as you age. If you have normal vision when you are young, you have a near point of 25 cm. A. If the distance between your eye's lens and retina is 1.69 cm, what is the focal length of your eye's lens when you look at an object at your near point? cm B. As you get older, suppose that the near point of your eye increases to 50 cm. What is the focal length of your eye's lens when you look at an object at your near point now? cm C. With your near point at 50 cm, what is the focal length of the corrective lens (placed directly in front of your eye's lens) which you would need to look at an object that is 25 cm in front of your eye? cm D. As you continue to age, the corrective lenses will no longer be sufficient to allow you to see an object that is 25 cm in front of your eye. When you are wearing your corrective lenses, suppose that you can now see objects only if they are no closer than 38 cm in front of your eye. What is the actual near point of your eye now? What is the focal length of your eye's lens that corresponds to this new near point? cm Submit Answer Save Progress

Explanation / Answer

A )

using equation

1/f = 1/u + 1/v

1/f = 1 / 25 + 1.69

f = 1.583 cm

b )

1/f = 1 /u + 1/v

1/f = 1/50 + 1/1.69

f = 1.634 cm

c )

1/f = 1/u + 1/v

1/f = 1/25 - 1/50

f = 50 cm

d )

1/50 = 1/N + 1/38

N = - 158.33 cm

1/f = 1/158.33 + 1.69

f = 1.672 cm

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