Q6 of 39 Page 35

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?


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.


More from this chapter

All 39 →
4

Explain this statement clearly:

“To call a dimensional quantity ‘large’ or ‘small’ is meaningless without specifying a standard for comparison”. In view of this, reframe the following statements wherever necessary:


A. Atoms are very small objects


B. A jet plane moves with great speed.


C. The mass of Jupiter is very large.


D. The air inside this room contains a large number of molecules.


E. A proton is much more massive than an electron.


F. The speed of sound is much smaller than the speed of light.

 5

A 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?

 7

A 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?

 8

Answer the following:

A. You are given a thread and a metre scale. How will you estimate the diameter of the thread?


B. A screw gauge has a pitch of 1.0 mm and 200 divisions on the circular scale. Do you think it is possible to increase the accuracy of the screw gauge arbitrarily by increasing the number of divisions on the circular scale?


C. The mean diameter of a thin brass rod is to be measured by Vernier callipers. Why is a set of 100 measurements of the diameter expected to yield a more reliable estimate than a set of 5 measurements only?