Question

Which of the following is the most precis device for measuring length:

(a) a vernier calipers with 20 divisions on the sliding scale?

(b) a screw gauge of pitch 1 mm and 100 divisions on the circular scale?

(c) an optical instrument that can measure length to within a wavelength of light?

Answer 1

An optical instrument which can measure length within a wavelength of light (=10^-6 m) is the most precise device for measuring the length.

So,(c) is the correct answer.