How much must the focal length of an eye change when an object, originally at 4.00 m, is brought to 40.0 cm from the eye? Assume a 2.5-cm distance between the eye lens and retina.

Question

Quizplus · Accepted Answer

The correct answer is A because the change in focal length is given by the formula:$$\Delta f = \frac{d_o d_i}{d_o - d_i}$$where $d_o$ is the original object distance, $d_i$ is the new object distance, and $d$ is the distance between the lens and the retina. Plugging in the given values, we get:$$\Delta f = \frac{(4.00 \ m)(0.400 \ m)}{4.00 \ m - 0.400 \ m} = 0.13 \ cm$$

How Much Must the Focal Length of an Eye Change