Physics · Measurements. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
No measurement is exact. A random error makes repeated readings scatter above and below the true value, so taking several readings and finding the mean reduces it. A systematic error shifts every reading the same way by the same amount, for example a zero error. Repeating does not help; you must find the error and apply a correction.
In this textbook, precision depends on the absolute uncertainty, which is the least count of the instrument. Accuracy depends on the fractional or percentage uncertainty, so a longer length measured with the same rule is more accurate.
When measurements are combined in a formula, their uncertainties are combined too, and the total is always larger.
When two quantities are subtracted, students subtract the uncertainties as well. Uncertainties never cancel: add the absolute uncertainties for both addition and subtraction.
Answer: 3%, so the area is 50 cm2 with an uncertainty of about 1.5 cm2
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