Focal Lens Question: A student is not capable of focusing on objects closer than

Question

Focal Lens Question:

A student is not capable of focusing on objects closer than 060m from the eyes and no farther than 1.lOm from them To improve the vision, separate prescriptions are needed. one to correct for myopia. and the other to correct for hyperopia a) What is in meters the focal length of the lens needed to enable the student to see objects that are 025m away from the eye? Express your answer in meters b) What is in diopters the power of that lens? c)What is in meters the focal length of the lens needed to correct for the myopia? Express your answer in meters What if we want to design a bifocal for the students. The top portion will allow him to see far away objects. The lens then will be the lens you calculated in part c. To be able to see objects that are 0.25m away from the eye. we need to glue another lens at the bottom portion of this lens d) What power lens should we glue to the lens you have determined in part c. to enable the student to see objects that are 025m away from the eye? Express your answer in diopters

Explanation / Answer

(A) Using the thin-lens equation for optical power-

P=O+I

P=1/0.60-1/0.25=-2.33

Focal length f=1/P= -0.42m.

(B) Power of that lens P=100/f (cm) =100/42= -2.33D.

(C) For correction og myopia-

P=O+I=1/0.60-1/1.10=0.75

Hence focal length f=1/P=1.32m

(D) power p=100/f(cm)=100/132=0.75D

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