Significant Figures

Significant Figures

Significant Figures

Question:   What is meant by the Significant Figures of a measurement. What are the main points to be kept in mind while determining the significant figures of a measurement?

Significant Figures

In any measurement the accurately known digits and the first doubtful digit are called significant figures. Significant figure gives the accuracy with which a physical quantity is expressed. The number of digits which are known reliably or about which we have confidence in our measurement plus the first digit that is uncertain are termed as significant figures.

For instance, the length of the table is 122.3 cm This has 4 significant figures and 3 is uncertain It is worth mentioning that significant figures of a physical quantity depend upon the least count of the instrument with which it is being measured.

Rules for Determining Significant Figures:

  • All the non-zero digits are significant For example 241.54 has five significant digits
  • All zeros occurring between two non-zero digits are significant For example 501.002 have six significant digits
  • The zeros occurring between the decimal point and the non-zero digits are not significant provided the integral part IS zero. For example 0.00243 has only significant digits
  • All zeros to the right of a non zero digit in a number written without a decimal point are not significant. For example 532.00 rave only three significant digits
    Exception:
    This rule does not work when we record the values on actual measurement basis. For example, distance between two places is 17.10 m. This figure has 4 significant digits.
  • All zeros occurring to the right of non-zero digit in a number written \4th decimal point are significant. For example 2.3200 has five significant digits.
  • The number of significant figures does not vary with choice of units. For example length of a rod is 82 cm. The number of significant figures remains 2 even if we represent it in meters or km that is 0.82 m or 0.00082 km. This signifies that the location of decimal point does not determine the number of significant figures by itself alone.
  • In exponent form, the exponential term does not contribute to the significant figures. Thus, 8.12×105 = 812000 which has only 3 significant figures.

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