Significant figures

 (A) Every scientific observation involves some degree of uncertainty depending upon the limitation of instrument. To represent scientific data, role of significant figures has its own importance.

 (B) Significant figures are equal to the number of digits in numbers with last digit uncertain and rest all are certain digits i.e. all the digits of datum including the uncertain one , are called significant figures. 

(C) Rules for determination of significant figure:

 (i) All non zero digits are significant.

 Example : 3.14 has three significant figures 

(ii) The zeros to the right of the decimal point are significant.

 Example : 3.0 has two significant figures.

 (iii) The zeros to the left of the first non zero digit in a number are not significant.

 Example : 0.02 has one significant figure.

 (iv) The zeros between two non zero digits are also significant.

 Example : 6.01 has three significant figures. 

(v) Exponential form : N × 10 n . Where N show the significant figure.

 Example : 1.86 × 10 4 has three significant figure.

 (vi) Rounding off the uncertain digit : 

(a) If the left most digit to be rounded off is more than 5 , the preceding number is increased by one. 

Example : 2.16 is rounded to 2.2

 (b) If the left most digit to be rounded off is less than 5 , the preceding number is retained.

 Example : 2.14 is rounded off to 2.1 

(c) If the left most digit to be rounded off is equal to 5 , the preceding number is not changed if it is even and increased by one if it is odd. Example : 3.25 is rounded off to 3.2 2.35 is round off to 2.4