The near point of a person's uncorrected eyes is 125.0 cm and the far point is at infinity.What is the focal length of a contact lens that will move the near point to 25.0 cm from this person's eyes?
A) -100 cm
B) -31.3 cm
C) 10.2 cm
D) 20.8 cm
E) 31.3 cm

Question

Quizplus · Accepted Answer

The formula for determining the focal length of a contact lens is:

1/f = 1/far point - 1/near point

We are given that the far point is at infinity, so we can simplify this to:

1/f = 0 - 1/125

Solving for f, we get:

f = -125

This means that a contact lens with a focal length of -125 cm would be needed to bring the near point to 125 cm. However, we want the near point to be 25 cm, so we need to adjust our formula:

1/f = 0 - 1/25

Solving for f, we get:

f = -25

So the focal length of the contact lens that will move the near point to 25 cm is -25 cm, or choice E.

The near Point of a Person's Uncorrected Eyes Is 125