Question

Which of the following is the most precise device for measuring length: a vernier callipers with 20 divisions on the sliding scale a screw gauge of pitch 1 mm and 100 divisions on the circular scale an optical instrument that can measure length to within a wavelength of light?

Answer 1

A device with minimum count is the most suitable to measure length.
Least count of vernier callipers
= 1 standard division (SD) – 1 vernier division (VD)

= 1-9/10=1/10 = 0.01 cm

Least count of an optical device = Wavelength of light ∼ 10^–5 cm
= 0.00001 cm
Hence, it can be inferred that an optical instrument is the most suitable device to measure length.