Which of the following is the most precise device for measuring length: (a) a vernier callipers with 20 divisions on the sliding scale (b) a screw gauge of pitch 1 mm and 100 divisions on the circular scale

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

(a) a vernier callipers 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 ?

Solution:

(a)Least count of vernier calipers = 1 /20  = 0.05 cm

(b) Least count of screw gauge =1/100 = 0.01 cm

(c) Least count of an optical device =1/ 10⁵ = 0.00001 cm

( Wavelength of light  =10^–5 cm)

Optical instrument has least count, Hence it is the most precise device for measuring length.