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Question 6

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 ?


A device with minimum count is the most suitable to measure length.

(a) Least count of vernier callipers

= 1 standard division (SD) -1 vernier division (VD)

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


(b) Least count of screw gauge = Pitch / Number of divisions

= 1/1000  = 0.001 cm


(c) 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.

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