MEASUREMENT OF PHYSICAL QUANTITIES IN CHEMISTRY

One of the important part of the scientific work is measuring of physical quantities such as mass, volume, length, energy, temperature, etc. It is interesting to note that all

these quantities can be expressed in terms of a few basic units. For example, in everyday life, we come across a number of measurements like kilograms (for mass), litres (for volume), metres (for length measurements) etc. In addition to these common measurements we need to measure a number of other quantities as concentration, temperature, pressure, density, amount of electrical charge etc.

“All such quantities which we come across during the Scientific studies are called 

physical quantities”.

A physical quantity thus refers to the result of measurement operation. 

It involves the comparison of the quantity to be measured with some fixed standard. 

  For example, if we are interested in Seal knowing the length of a pencil, the operations would be:

(i) to lay the pencil parallel to centimeter scale and

(ii) to count the number of markings on the scale.

Suppose the number of markings is 9.5. This implies that the piece of paper is 9.5 times longer than one unit of measurement. It makes no sense to say that length of paper is 9.5. However, if we attach centimetre, a unit of length, to the numerical figure, i.e., 9.5 cm, it will become more appropriate. Thus, a measured physical quantity is expressed in two parts, a numerical coefficient and a unit. 

Either of them is meaningless without the other.

In the measurement of the length of the pencil, 9.5 is a numerical figure whereas centimeter is a unit.

The study of experimental science thus depends upon the quantitative measurement of properties. Every measurement gives a numerical result that has three important aspects:

(i) Numerical magnitude,

(ii) Accuracy or precision with which the number is expressed and

(iii) Indicator of scale i.e., unit employed to express.

The measurement of physical quantities becomes scientifically more correct and relevant if all the three aspects as given above are reported. Thus,

“A unit may be defined as the standard of reference chosen to measure or express any physical quantity”.