Units and Measurement
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Question : 6
Total: 33
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) 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:
The most precise device is that whose least count is minimum.
Now :
(a) Least count of vernier callipers = 1 MSD – 1 VSD
= 1 M S D −
M S D
=
M S D =
m m
=
c m = 0.005 c m
(b) Least count of screw gauge
=
=
m m
=
c m
= 0.001 c m
(c) Wavelength of light,λ ≃ 10 – 5 c m = 0.00001 c m
∴ Least count of optical instrument= 0.00001 c m
Thus, clearly the optical instrument is the most precise.
Now :
(a) Least count of vernier callipers = 1 MSD – 1 VSD
(b) Least count of screw gauge
(c) Wavelength of light,
∴ Least count of optical instrument
Thus, clearly the optical instrument is the most precise.
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