What is the focal length of a one diopter lens?

The focal length of a lens is related to its power, measured in diopters. Specifically, the power (P) of a lens in diopters is defined as the reciprocal of its focal length (f) in meters. This relationship can be represented by the formula:

[ P = \frac{1}{f} ]

For a one diopter lens, the power (P) is 1 diopter. To find the focal length, you can rearrange the formula:

[ f = \frac{1}{P} ]

Substituting the power of the lens:

[ f = \frac{1}{1 \text{ diopter}} = 1 \text{ meter} ]

This indicates that a lens with a power of one diopter has a focal length of 1 meter. Thus, the correct answer reflects this calculation. It's important to note that while the power of a lens increases as the focal length decreases, in this instance, for a one diopter lens, the focal length is specifically 1 meter.