- If Michaela needs to wear reading glasses with refractive power of +2.8 D, wha

Question

- If Michaela needs to wear reading glasses with refractive power of +2.8 D, what is her uncorrected near point? Neglect the distance between the glasses and the eye. Assume that the distance from the cornea-lens system to the retina is 2.1 cm and the normal near point is 30 cm.
___ m

-The uncorrected far point of Charlotte's eye is 2.7 m. What refractive power contact lens enables her to clearly distinguish objects at large distances? Assume that the distance from the cornea-lens system to the retina is 2.0 cm and the normal near point is 28 cm.
___ D

Explanation / Answer

Answer:-

Part A:- Refractive Power (P) = +2.8 D

P = 1/f

Distance from the cornea-lens system to the retina = 2.1 cm

Distance from the cornea-lens system to the normal near point = 30 cm

Uncorrected near point: 1/d(unc) + 1/0.021 = 1/f(eyelens) -----(1)

Corrected near point: 1/d(corr) + 1/0.021 = 1/f(eyelens) + 1/f(corr. lens)  -----(2)

Using (1) and (2) we get,

=> 1/d(unc) = 1/d(corr) - 1/f(lens)

=> 1/d(unc) = 1/0.30 - 2.8

=> 1/d(unc) = 3.3333 -2.8

=> 1/d(unc) = 0.5333

=> d(unc) = 1.875 m

Distance between the glasses and the eye  = 1.875 m

Part B:-

Uncorrected far point of Charlotte's eye = 2.7 m

Distance from the cornea-lens system to the retina = 2.0 cm

Distance from the cornea-lens system to the normal near point = 28 cm

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