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?
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Answer:
(a) Least count of this vernier callipers = 1SD - 1 VD = 1 SD - 19/20 SD = 1/20 SD
= 1.20 mm = 1/200 cm = 0.005 cm
(b) Least count of screw gauge = Pitch/Number of divisions = 1/1000 = 0.001 cm.
(c) Wavelength of light, λ ≈ 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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