Question

Contact lenses are placed right on the eyeball, so the distance from the eye to an object (or image) is the same as the distance from the lens to that object (or image). A certain person can see distant objects well, but his near point is 50.0 cm from his eyes instead of the usual 25.0 cm .

Part A

Is this person nearsighted or farsighted?

Is this person nearsighted or farsighted?

This person is nearsighted.

This person is farsighted.

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Part B

What type of lens (converging or diverging) is needed to correct his vision?

What type of lens (converging or diverging) is needed to correct his vision?

A converging lens is needed to correct his vision.

A diverging lens is needed to correct his vision.

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Part C

If the correcting lenses will be contact lenses, what focal length lens is needed ?

f =

  cm  

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Part D

What is the power corresponding to the focal length found in part (C) in diopters?

D =

  diopters  

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Answer 1

A) Far sighted

B) Converging lens

C) near point hyperopic eye is s¹ = - 50 cm

   s = 25 cm

we determine the required focal length of the contact lens using the object image relation ship.

   1/f = 1/s + 1/s¹

         = 1/ 25cm - 1/50cm

       f = + 50 cm

we need to converging focal length with f = 50 cm

D) the corresoponding power is

        p = 1/f

            = 1/0.5 m

            = + 2.0 diopters