Work out the lens powers

Exercise and reference answers

Questions

1. Answer

   1

   Question

   Power in dioptre of a lens of focal length 1 m?

2. Answer

   40

   Question

   Focal length in cm of a plus 2.5 D lens?

3. Answer

   25

   Question

   Focal length in cm of a minus 4.0 D lens?

Instructions

Type the number only.

Explanation