Difference between accuracy and precision with example

We often hear the words accuracy and precision in measurement of a physical quantity during an experiment. Most of the students feel that these two terms have the same meaning. But these are much different. In this article, we are going to discuss the concepts and difference between accuracy and precision with example of experimental data.

Contents in this article:

  1. What is accuracy of a measurement?
  2. What is precision measurement?
  3. Explanation of accuracy and precision with example of experimental data
  4. Difference between accuracy and precision in a measurement

What is accuracy of a measurement?

The accuracy of measurement of a physical quantity indicates how closer is the measured value of the physical quantity to its actual value or true value. To obtain greater accuracy, the average of the measured values should be very closer or nearly equal to the actual value of the physical quantity.

What is precision measurement?

Precision measurement of a physical quantity indicates how closer are the measured values to each other. During the measurement of a physical quantity, we often measure more than once (usually we take three or five observations). If these data are very close to each other then the measurement is a precision measurement. This is the basic concept and definition of precision in physics.

Explanation of the terms accuracy and precision with example of experimental data

Let, we are measuring the length of a rod whose actual length is 100.0 meter. Here, we are using a measuring scale which can measure up to one decimal. Three students measured the length of the rod with same type of measuring scales. Measured data are shown in the table below –

No. of observationData of Student-1Data of student-2Data of student-3
1100.8101.1100.1
299.8100.999.9
399.4101.1100.0
4100.1101.2100.1
5100.5101.0100.2

The average value of the data of student-1 is 100.1 meter which is very much closer to the actual value 100.0 meter. So, the measurement of the student-1 is accurate. But the if we look the data carefully, we can see that the data are not closer to each other, they have wide differences by 1.4 meter, 1.1 meter, etc. So, the measured data of student-1 is not precise. Hence, the measurement of student-1 is accurate but not precise.

The average value of the data of student-2 is 101.1 meter which has 1.1 meter difference from the actual value 100.0 meter. So, the measurements of student-2 have not a good accuracy. But all measurements are very close to each other. The differences between the data are 0.1, 0.2, etc. So, the measurement of student-2 is a precision measurement.

Similarly, we can see that the measurement of student-3 has higher accuracy with good precision.

What is the difference between accuracy and precision?

The differences of accuracy and precision are as followings –

  1. Any measurement closer to the actual value is an accurate measurement. If the measured values are closer to each other then the measurement is a precise measurement.
  2. Accuracy of a measurement can be identified even after taking a single observation. But the precision of measurement can be identified only after taking two or more observations.
  3. Systematic errors cause less accuracy. Random errors cause poor precision.

People also ask:

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This is all from this article on accuracy and precision of measurement. If you have any doubt on this topic you can ask me in the comment section.

Thank you!

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