NCERT Solutions Class 11 Physics - Solved Exercise Question 2.6

Question 2.6:

Which of the following is the most precise device for measuring length :
(a) a vernier caliper 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 device with minimum count is the most suitable to measure length.
(a) Least count of vernier calipers
= 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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