E1.1 Precision & Significant Figures:

Precision:

The measurement of a physical quantity is never absolutely correct. It cannot be measured exactly, no matter what measuring device is used. It is correct to certain limit which is called the precision limit. The precision limit depends on the list count of measuring instrument. For example:

A mechanical watch can measure smallest value generally not less than one second. But a digital watch can measure even a fraction of a second. Thus, such a digital watch is more precise than mechanical watch. Similarly, a micrometer-screw gauge has least count 0.01mm or smaller than this value, which is very precise than a meter scale.

Significant figures: 

Any measurement of a physical quantity is an attempt to determine its true value. The measured value of a physical quantity tells the number of digits in which we have confidence. 

In the measurement of a physical quantity the number of meaningful digits in the stated value of the quantity is called the significant figures.

Rules for deciding the significant digits:

- Numbers with no decimal points: All digits (non-zero & zeros) are significant except zeroes at the beginning and end of a number.

Example: 23456: five significant figures 

                89760054: Eight significant figure 

                0004567360000: Six significant figure

- Numbers with decimal points: 

All non-zero digits (before and after decimal point) are significant.

         Example: 987.654 : six significant figures

All digits (zeros & non-zeros) to the right of a non-zero digit are significant.

         Example: 5.00 : three significant figures

                          0.1000 : four significant figures 

                          0.00250 : three significant figures

Return to Main Menu