What is the focal length of 1.75 D reading glasses found on the rack in a pharmacy?

Video Transcript

This is College Physics Answers with Shaun Dychko. Some reading glasses in a pharmacy have a power of 1.75 diopters and we want to figure out what is its focal length. So the power in diopters is the reciprocal of focal length in meters and we can figure out what f is by multiplying both sides by f divided by P so the focal length is the reciprocal of the power. So that's 1 over 1.75 diopters and that works out to 0.5714 meters and we can multiply that by 100 centimeters for every meter and this is 57.1 centimeters is the focal length.