question_answer 6)

Which of the following is the most precise device for measuring length: (a) a vernier calliper 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 visible light ?  

Answer:

The device that has minimum least count will be more precise for measuring length. (a) Least count of vernier callipers   . (b) Least count of screw gauge   (c) Least count of optical instrument = Wavelength of visible (red) light   = 0.00006 cm. Hence the most precise device for measuring length is the given optical instrument.