# NCERT Class 11 Physics Solutions: Chapter 2-Unit and Measurement Part 5

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Question: 2.7

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 on the thickness of hair?

• Magnification of the microscope = 100

• Average width of the hair in the field of view of the microscope = 3.5 mm

Actual thickness of the hair is

• Microscope looks like

Question: 2.8

(a) You are given a tread 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 calipers. Why is a set of 100 measurements of the diameter expected to yield a more reliable estimate than a set of 5 measurements only?