Units of Measurement

The comparison of an unknown quantity with a known fixed quantity of the same kind in called measurement. The known fixed quantity is called unit.

Measurement without units of a physical quantity has no meaning. i.e.  If we say the length of a room is 17. Then it has no meaning.  But if we say the length of a room is 17 feet. Then it represent a meaningful sense about the room.

Types of units

Units are divided into two types

Fundamental units:

Those units are independently measure a physical quantity is known as fundamental units.

The units of the measurement of the length, mass and time are not dependent to each other. Therefore, those units are known as fundamental units.

Derived Units:

Some of the units are developed by the use of one or more fundamental units are known as Derived Units.

e.g. the area of a rectangle field is define as multiplication of length and breadth of the field. Here the unit of the area is known as Derived units.

Unit of the area = unit of the length x unit of the length = (unit of the length)².

Different System of fundamental units

We can use three different system to describe the fundamental units are

• Matric system or C.G.S system (Centimetre Gram Second)
• F.P.S System (Foot-Pound- Second)
• M.K.S System (Metre-Kilogram-Second)

In the earlier age different unit systems are followed for measurement of same physical quantity. To create a standard procedure, scientists are developing another system of unit called System de International or S.I in the year 1960.

Note : S.I System was introduce by the following organisation

1. International Union of Pure and applied chemistry (I.U.P.A.C.)
2. International organisation for standardisation.

Fundamental units of the S.I System

Units of the 7 physical quantities are defining as fundamental units in S.I. system.

Derived Units of the S.I. System

Light year

In vacuum medium, total distance travel by the light in a year is known as light year. This unit is used for measure the long distance in the universe. 

Note:   1 lightyear = 9.45 x 10¹² kilometer(eprox.)