A farsighted eye is corrected by placing a converging lens in front or the eye.

Question

A farsighted eye is corrected by placing a converging lens in front or the eye. This results in a virtual image located at the eye's near point, the distance to the closest object that can be seen clearly in focus by the eye (normally taken to be about 25.0 cm for someone with perfect eyesight). However, if a person has a near point of 71.5 cm, what focal length should contact lenses have to treat this farsightedness? For contact lenses, the distance from the eye to the contact lens is negligible. Focal length of lenses What is the corresponding power of the contact lenses? Power of lenses

Explanation / Answer

image distance, q = -71.5 cm

object distance, p = 25 cm

Applying 1/f = 1/p + 1/q

1/f = 1/25 + 1/-71.5

f = 38.44 cm ......Ans

P = 1/f = 1/(0.3844 m)

P = 2.60 D ......Ans

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