Profile
Settings
Refer your friends
Sign out
To measure any given object, we need its unit. It isn’t easy to relate and understand the quantitative value without units. In 1960 with the rapid growth of science and technologies, scientists decided to have a universal system of units to avoid confusion due to units. Thus, they decided on the International System of units to be a universal metric system of measurement.
Other measurement systems like the imperial system of measurement were earlier used in the US, but only the SI unit dominates the global academia. 7 base units make up the SI units list; this inturn forms 22 derived units.
What is an SI unit?
SI unit is a metric system used globally to measure any item. These units are based on standard metric units to understand the unit system globally. This international system is based on the MKS system of units.
SI base units
The SI units have 7 base units that behave as the primary unit of any metric scale. These units are independent metric units that do not depend on other units to derive them. These fundamental units are necessary to measure any entity. The table below lists the SI base units.
| S.No | Base Quantity | Base Unit | Symbol |
| 1 | Length | metre | m |
| 2 | Mass | kilogram | k |
| 3 | Time | second | s |
| 4 | Electric current | ampere | A |
| 5 | Thermodynamic temperature | kelvin | K |
| 6 | Amount of substance | mole | mol |
| 7 | Luminous intensity | candela | cd |
Unit of length:
The unit of length is a metre, and the symbol is ‘m’. A metre is defined as the fixed numerical value of the distance light travels in a vacuum.
Unit of mass:
The unit of mass is the kilogram, and its symbol is ‘kg’. A kilogram is defined by taking the fixed numerical value of the Planck constant.
Unit of time:
The unit of time is second, and the symbol is ‘s’. A second is defined by taking the fixed numerical value of caesium frequency.
Unit of electric current:
The unit of electric current is the ampere, and its; symbol is A. An ampere is defined by taking the fixed numerical value of the elementary charges.
Unit of thermodynamics temperature:
The unit of thermodynamics temperature is kelvin, and the symbol is K. A kelvin is defined by taking the fixed numerical value of the Boltzmann constant. It is expressed in the unit kg m2 s-2K-1.
Unit of the amount of substance:
The unit of the amount of substance is mole, and the symbol is ‘mol’. A mole is defined by taking the fixed numerical value of the Avogadro constant. It is expressed in the unit mol.
Unit of luminous intensity
The unit of luminous intensity is candela, and the symbol is cd. A candela is defined by taking the fixed numerical value of luminous efficacy.
SI derived units:
SI-derived units are derivatives of the SI base units included in the international system of units. These derived units are not capable of existing independently. They are dimensionless and formed when one or more base units combine. There are 22 types of derived units included in the SI units list. These Si-derived units are given unique names like hertz (Hz), a unit of frequency.
In physics, SI units and their derivations must be written in lowercase. In certain exceptional cases, when the unit is a proper noun, like in the case of hertz, the symbol is denoted with a capital letter (Hz).
Here is the complete table of 22 derived SI units list:
| S.No | Quantity | Unit | Symbol |
| 1 | Frequency | hertz | Hz |
| 2 | Angle | radian | rad |
| 3 | Solid angle | steradian | sr |
| 4 | Force, weight | newton | N |
| 5 | Pressure, stress | pascal | Pa |
| 6 | Energy, work, heat | joule | J |
| 7 | Power, radiant flux | watt | W |
| 8 | Electric charge | coulomb | C |
| 9 | Voltage | volt | V |
| 10 | Electrical capacitance | farad | F |
| 11 | Electrical resistance | ohm | Ω |
| 12 | Electrical conductance | siemens | S |
| 13 | Magnetic flux | weber | Wb |
| 14 | Magnetic induction | tesla | T |
| 15 | Electrical inductance | henry | H |
| 16 | Temperature | Degree celsius | °C |
| 17 | Luminous flux | lumen | lm |
| 18 | Illuminance | Lux | lx |
| 19 | Radioactivity | Becquerel | Bq |
| 20 | Absorbed dose | Grey | Gy |
| 21 | Equivalent dose | Sievert | Sv |
| 22 | Catalytic activity | Katal | kat |
Advantages of SI units
In physics SI units and their derived units are vital, but apart from that, using this metric system also has other pros. The main reasons for using SI units are that they are rational, metric, and coherent. The system has only one unit for a quantity, it is multipliable in powers of ten, and it has basic fundamental units that derive from other units. These reasons make this system universal and efficient.
Conclusion
As we acknowledge the SI unit and its importance, we must also recognise its derivatives and uses. These units build up the entire system of physics and its application. Scientists are using these metrics to relate the observation and results of various experiments and research all around the globe. SI units are the essential pillars in the system of measurements as they pave the way for a uniform understanding of the concepts. Having a rigid unit for a quantity makes it easy to observe the result and research accordingly. Undoubtedly, these SI units are the fundamentals for the system of measurements.
