What power contact lens should be used to correct the vision of a farsighted person whose near point is 80 cm so she can see things clearly that are 25 cm in front of her?
A)+2.8 diopters
B)-2.8 diopters
C)-4.0 diopters
D)-4.2 diopters
E)+4.2 diopters

Question

Quizplus · Accepted Answer

The power of the contact lens is given by the formula:P = 1/f (in diopters)where f is the focal length of the lens in meters.The near point of the farsighted person is 80 cm, so the focal length of the lens needed to correct their vision is:f = 1/P = 1/2.8 = 0.36 mThe person wants to be able to see things clearly that are 25 cm in front of them, so the image distance is:d = 25 cm = 0.25 mThe lens equation is:1/f = 1/d + 1/Dwhere D is the distance between the lens and the retina.Substituting the values we know into the lens equation, we get:1/0.36 = 1/0.25 + 1/DSolving for D, we get:D = 0.45 mThe power of the contact lens is therefore:P = 1/f = 1/0.36 = +2.8 dioptersTherefore, the correct answer is A.

What Power Contact Lens Should Be Used to Correct the Vision