What is the focal length of 1.75 D reading glasses found on the rack in a pharmacy?
Question by OpenStax is licensed under CC BY 4.0
Final Answer

57.1 cm57.1\textrm{ cm}

Solution video

OpenStax College Physics for AP® Courses, Chapter 25, Problem 38 (Problems & Exercises)

OpenStax College Physics, Chapter 25, Problem 38 (PE) video thumbnail

In order to watch this solution you need to have a subscription.

Start free trial Log in
vote with a rating of votes with an average rating of .

Calculator Screenshots

  • OpenStax College Physics, Chapter 25, Problem 38 (PE) calculator screenshot 1
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.