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Q1.8: NCERT Physics - Part 1 UNITS AND MEASUREMENT 1.8 Solution: Answer the following: (a) You are given a thread and a metre…
⚠️ Common Exam Traps & Conceptual Pitfalls
Students often assume that increasing the number of divisions on a measuring instrument's scale indefinitely will improve accuracy, ignoring that precision is fundamentally limited by the instrument's pitch and the human eye's ability to resolve distinct divisions.
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?
Step-by-Step Verified Solution
**Answer:** (a) Wind the thread tightly on a pencil, measure total width, divide by number of turns. (b) No. (c) More measurements reduce random error.
**Step-by-Step Explanation:**
(a) Wind the thread closely on a pencil or cylindrical rod for several turns. Measure the total length of the winding with a metre scale. Divide by the number of turns to get the diameter.
(b) No, accuracy cannot be increased arbitrarily. The least count is limited by the pitch and the practical ability to read the circular scale. Also, the screw may have manufacturing defects.
(c) More measurements reduce the random error. The mean of 100 readings is more reliable (standard error ) than the mean of 5 readings.
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