Q. 64.4( 34 Votes )
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?
Answer :
In this question, three measuring/ calibrating instruments are given. Among these devices, we have to find the most precise device.
To find the most precise device we have to calculate the Least Count of these devices.
(a). Least count of Vernier calliper = 
= 
= 0.05 mm
= 0.05 cm
(b). Least count (L.C) of screw gauge = 
Pitch = 1 mm
No. of division on circular scale = 100
L.C = 1 × 10-3 × 
= 0.01 cm
(c). Least count of optical instrument that can measure length to within a wavelength of light is about 0.00001 cm
Here optical instrument has least count among given instruments. So Optical instrument is the most precise device for measuring length.
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PREVIOUSA new unit of length is chosen such that the speed of light in a vacuum is unity. What is the distance between the Sun and the Earth in terms of the new unit if light takes 8 min and 20 s to cover this distance?NEXTA student measures the thickness of a human hair by looking at it through a microscope of magnification 100. He makes 20 observations and finds that the average width of the hair in the field of view of the microscope is 3.5 mm. What is the estimate of the thickness of hair?
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