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Question 2: Define the terms error, uncertainty, precision and accuracy in measurement.



Error is the difference between the true value of the quantity being measured and the experimentally measured value by the experimenter.

Although it is not possible to completely eliminate errors from a measurement, however, it is possible to control or minimize it.


Uncertainty is the part of the reported value that characterizes the range within which the true value of the quantity is asserted (asserted means certain or sure) to lie.

Let the length of a block is 22.5 cm. Least count of the meter rid is 0.1 cm, which is equal to the absolute uncertainty. The length of the block is then, 22.5±0.1 cm. Therefore, the uncertainty lies in the range of ±0.05 cm. The true value lies within this range such that it may be 22.4 cm or 22.6 cm or any value from 22.4 cm to 22.6 cm.


Precision is the closeness of two or more than two measurements with each other. It should be noted that the measurements should be made under same conditions.

Note that it does not mean accuracy rather it is associated with the least count of the instrument used for measurement.


Accuracy is the closeness of the measured value to the standard value.

Accuracy is associated with the magnitude of fractional or relative error in the measurement.

Relative error is (total error/value of the measurement)