System of units
It is a system in which units are well defined and acceptable internationally or locally.
Generally, there are four System of units :
FPS system or British system
CGS system
MKS system
International system of unit ( SI )
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FPS system or British system
In this system the unit of length is foot , the unit of mass is pound , and the unit of time is second.
It is also known as British system.
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CGS system
In this system the unit of length is Centimetre , the unit of mass is Gram , and the unit of time is Second.
MKS system
In this system the unit of length is Metre , the unit of mass is Kilogram , and the unit of time is Second.
It is a metric system.
International system of unit ( SI )
SI unit is an international system of measurements that are used universally in all field to avoid the confusion with the units. This system is the modified form of MKS system and hence it is also known as rationalised MKS system. In SI, there are seven fundamental and two supplementary units.
There are seven fundamental unit .
| s.no. | Unit | physical quantity |
|---|---|---|
| 1. | Kilogram | Mass |
| 2. | Metre | Length |
| 3. | Second | Time |
| 4. | Kelvin | Temperature |
| 5. | Ampere | Electric current |
| 6. | Mole | Quantity of matter |
| 7. | Candela | Luminous intensity |
Supplementary unit
| s.no. | physical quantity | name of unit |
|---|---|---|
| 1. | Phase angle | Radiun |
| 2. | Solid angle | Steradian |
Advantage of SI system
The system of unit is internationally accepted.
In SI system the total number of units are small.
This system of unit is metric system ( I.e. can expressed in power of 10 ).
It is a rational system of unit . ( i.e. it uses only one unit for a given physical quantity . example joule is the unit of all types of energy. )
It is a coherent system of unit. ( i.e. obtained by multiplying or dividing the set of basic or fundamental unit. )