SI units, an abbreviation of the French term Système International, constitute the universally accepted metric system of measurements. They serve as the standard units for scientific and technological research and development, ensuring consistency and precision. The system comprises 7 base units that define 22 derived units. The SI units can be represented either as standard multiples or fractional quantities. These quantities are specified using prefix multipliers with powers of 10 that range from 10-24 to 1024.
The SI unit is an international system of measurements that is used universally in technical and scientific research. It standardizes the measurements used, ensuring that they are understood and interpreted consistently across the globe. The following table lists the base SI units:
Sl. No.
Name of the Quantity
SI Unit
SI Unit Symbol
1.
Length (l)
Meter
m
2.
Mass (M)
Kilogram
kg
3.
Time (T)
Second
s
4.
Electric current (I)
Ampere
A
5.
Thermodynamic temperature (Θ)
Kelvin
K
6.
Amount of substance (N)
Mole
mol
7.
Luminous intensity (J)
Candela
cd
What is SI Units List?
There are several SI units used in physics to represent different quantities. These quantities can be classified into two categories: base units and derived units.
SI Base Units
These are the fundamental units that serve as the building blocks of the system. All other units are derived from these SI Base units. For example, the SI unit of mass is kilogram, which is often confused with grams.
SI Base Units List
There are 7 SI base units. The seven units along with their SI unit and symbol are provided below:
Unit of length, meter (m): Meter is the SI unit of length. It is defined by taking the fixed value of the speed of light in vacuum and is expressed as m.s-1.
Unit of mass, kilogram (kg): Kilogram is the SI unit of mass. It is defined by taking the fixed value of the Planck constant and is expressed as kg.m2.s-1.
Unit of time, second (s): Second is the SI unit of time. It is defined by taking the fixed value of Cesium frequency and is expressed as s1.
Unit of electric current, ampere (A): Ampere is the SI unit of electric current. It is defined by taking the fixed value of the elementary charge.
Unit of thermodynamic temperature, Kelvin (K): Kelvin is the SI unit of thermodynamic temperature. It is defined by taking the fixed value of the Boltzmann constant, k = 1.380649×10-23.
Unit of the amount of substance, mole (mol): Mole is the SI unit of the amount of substance. It is defined by the fixed value of Avogadro constant, NA. One mole contains 6.02214076×1023 elementary entities and is expressed as mol-1.
Unit of luminous intensity, candela (cd): Candela is the SI unit of luminous intensity. It is defined by the fixed value of the luminous efficacy.
Note: These 7 units are assumed to be mutually independent, hence they are referred to as base units.
SI Derived Units
The derived units are unlimited as they are formed by different operations on the base units. For derived units, the dimensions are expressed in terms of the dimensions of the base units. The derived units might also be expressed with the combination of base and derived units.
SI Derived Units List
There are several derived units in physics. Some of the most commonly used SI derived units in physics are given below.
Sl. No
Unit(s) Name
SI Unit
SI Unit Symbol
Expressed in SI Base Unit
Expressed in other SI units
1.
Force, Weight
Newton
N
kg⋅m⋅s-2
-
2.
Frequency
Hertz
Hz
s-1
-
3.
Electric charge
Coulomb
C
s⋅A
-
4.
Electric potential (Voltage)
Volt
V
kg.m2.s-3.A-1
W/A
5.
Inductance
Henry
H
kg.m2.s-2.A-2
Wb/A
6.
Capacitance
Farad
F
kg−1.m−2.s4.A2
C/V
7.
Resistance, Impedance, Reactance
Ohm
Ω
kg.m2.s−3.A−2
V/A
8.
Electrical conductance
Siemens
S
kg−1.m−2.s3.A2
Ω−1
9.
Magnetic flux
Weber
Wb
kg.m2.s−2.A−1
V⋅s
10.
Magnetic flux density
Tesla
T
kg.s−2.A−1
Wb/m2
11.
Energy, Work, Heat
Joule
J
kg.m2.s−2
N⋅m = Pa⋅m3
12.
Power, Radiant flux
Watt
W
kg.m2.s−3
J/s
13.
Angle
Radian
rad
m.m−1
-
14.
Radioactivity
Becquerel
Bq
s-1
-
15.
Luminous flux
Lumen
lm
cd
cd⋅sr
These are just a few of the many derived units used in physics. Additional units include momentum (P) with the SI unit of kilogram meter per second (kg⋅m/s), the magnetic field (B) measured in Tesla, heat measured in Joules, and velocity expressed in m/s. To perform well in physics examinations, students need to be familiar with both the CGS and SI units.
It is crucial to remember that in an examination, an answer is considered incomplete without its corresponding unit.
The SI units form an integral part of physics. In addition to the units mentioned above, there are several other units that are frequently encountered in physics. Some of these include:
The SI unit of momentum (P) is kilogram meter per second (kg⋅m/s)
The SI system is based on precise and definite standards. The base used in the SI system is 10, which makes the conversion easier. Latin and Greek prefixes are used in the SI system and these refer to the numbers. Without the use of conversion factors, the SI units can be derived from one another.
What are the common System of Units used in measurements?
The commonly used System of Units in measurements are the CGS system, MKS system, and SI system.
Define unit.
Unit is defined as the reference standard used for measurements.
Name the fundamental physical quantities.
There are seven fundamental physical quantities: length, mass, time, electric current, temperature, amount of substance, and light intensity.