Question

What do you mean by units? Study about the different types of units.

Answer 1

Hint: This question is from chapter “units and measurement”. After giving proper definition of units, classify them into different categories like fundamental units and derived units and give examples of each.
In measuring any quantity, units are always used. Therefore units have wide applications in our day to day life. For e.g. in measuring milk, oil etc litre (l) is used as a unit or in measuring sugar, floor, fruits etc kilogram or gram is used as a unit.

Complete step by step solution:
Unit: - Measurement of any physical quantity involves comparison with a certain basic, arbitrarily chosen, internationally accepted reference standard called unit. The result of a measurement of a physical quantity is expressed by a number (or numerical measure) accompanied by a unit.
For example, 5 kg
In this 5 is numerical value and kg is the unit.
Classification of units: -Units are further classified into two categories,
Fundamental units
 Derived units
The units for the fundamental or base quantities are called fundamental or base units. For e.g. kg for mass, seconds for time etc.
The units of all other physical quantities can be expressed as combinations of the base units. Such units obtained for the derived quantities are called derived units. For e.g. Velocity is a derived quantity, i.e. derived from other fundamental quantities and its units $ m{{s}^{-1}} $ are derived units.
  In earlier times scientists of different countries were using different systems of units for measurement.
• In the CGS system they were centimetre, gram and second respectively.
• In the FPS system they were foot, pound and second respectively.
• In the MKS system they were metre, kilogram and second respectively.
• SI system of units: - It is presently used as a system of units that is accepted internationally. E.g. meter, kilogram, seconds are used for length, mass, and time respectively.

Note:
In SI, there are seven base units as given in table below,

Base quantity	Name	Symbol
Length	metre	m
Mass	kilogram	kg
time	second	s
Electric current	ampere	A
Thermodynamic temperature	kelvin	K
Amount of substance	mole	mol
Luminous intensity	candela	cd