MEASUREMENT AND THEIR DEVICES

SYSTEM OF MEASUREMENT AND MEASURING DEVICES

By saying measurement a question arise in the mind that what is measurement?. The answer is as simple is that measurement is the numerical value multiplied by its unit.


Lets begin our study.

Some basic knowledge you have to acquire.


What is physical Quantity?


The quantities which we can measure are called physical quantity.

It is the measurable property of a matter. As per example, length, mass, density, velocity are all physical quantity because they all can be measured .For the measurement of a physical quantity we must know two basic things.


(i)The unit in which the quantity is to be measure

Example: If we have 10 kg of mangoes and we are measuring in litre  it is not the right process we have to measure it in the unit of Kg not in liter. 


(ii) The numerical value which express how many times the unit used

       is contained the given quantity.


What is unit?


To measure any physical quantity, we must first have a unit of measurement. By unit of a physical quantity we mean a definite and convenient amount of that quantity. The magnitude of a physical quantity is obtained by comparing it with the unit.The factor by which a quantity is bigger or smaller than the corresponding unit is called the numerical measurement of that quantity. As  per example “a room is 5  metre  long clearly showing that the physical quantity being measured is length, and the unit chosen  for measuring the room is metre and the numerical value  is 5.


In the previous para we have seen that the unit of length is metre. But what is a metre? To define it we evidently require a standard length. Similarly we require a standard for every other unit. A standard is the physical embodiment of a unit. It fixes up and preserves the size of the corresponding unit. A unit may be of same size as that of the standard or may me a multiple or submultiple of it. The standard Proto-type of kilogram is the standard of  mass, the units of mass being kilogram(kg.), metric ton(10³kg.), gram(10^-3kg.) etc.



All physical quantities have units?


The answer or this question is as simple is that there are many physical quantities which does not have any units .The question arise in the mind that if a thing is in the category its first condition is that it would be measurable

And for measuring a unit is required so how a quantity is physical but not measurable . As in the field of physics there are some physical quantities that does not have any units there are the exceptions  like six fingers in one hand of a human ,The reason is that for a non-unit physical quantity that those physical quantities which are expressed as the ratio of the same physical quantity do not have units .

Example : atomic weight of elements, specific gravity, refractive index.