Question

Describe what is meant by significant figures.

What do you mean by significant figures?

Answer 1

Significant figures:

1. Significant figures in the measured value of a physical quantity are the sum of reliable digits and the first uncertain digit. 
                                OR
   The number of digits in a measurement about which we are certain, plus one additional digit, the first one about which we are not certain, is known as significant figures or significant digits.
2. The larger the number of significant figures obtained in a measurement, the greater is the accuracy of the measurement. The reverse is also true.
3. If one uses the instrument of the smallest least count, the number of significant digits increases.

Rules for determining significant figures:

1. All the non-zero digits are significant; for example, if the volume of an object is 178.43 cm³, there are five significant digits, which are 1, 7, 8, 4, and 3.
2. All the zeros between two nonzero digits are significant; e.g., m = 165.02 g has 5 significant digits.
3. If the number is less than 1, the zero/zeroes on the right of the decimal point and to the left of the first nonzero digit are not significant, e.g., in 0.001405, the underlined zeroes are not significant. Thus the above number has four significant digits.
4. The zeroes on the right-hand side of the last nonzero number are significant (but for this, the number must be written with a decimal point), e.g., 1.500 or 0.01500 both have 4 significant figures each. 
   On the contrary, if a measurement yields length L given as L = 125 m = 12500 cm = 125000 mm, it has only three significant digits.

Answer 2

1. Significant figures are those meaningful digits that are known with certainty.
2. They indicate uncertainty in an experiment or calculated value. For example, if 15.6 mL is the result of an experiment, then 15 is certain while 6 is uncertain, and the total number of significant figures is 3.
3. Hence, significant figures are defined as the total number of digits in a number, including the last digit that represents the uncertainty of the result.