Contact lenses are placed right on the eyeball, so the distance from the eye to

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. Is this person nearsighted or farsighted? This person is nearsighted. This person is farsighted. 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. If the correcting lenses will be contact lenses, what focal length lens is needed ? f = cm What is the power corresponding to the focal length found in part (C) in diopters? D = diopters

Explanation / Answer

A)This person is farsighted.

B)A converging lens is needed to correct his vision.

C)from lens eqn we know

1/f = 1/s + 1/s'

f = ss'/(s - s')

f = 25 x 50/(25 - 50) = 50 cm

Hence, focal length = 50 cm

D)Power is inverse of focal length

P = 1/0.5 = 2 Diopters

Hence, P = 2 Diopters

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