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Physics is a vast subject and its physical quantity that we use is expressed in terms of any particular units. The question that comes to mind is “ What do you understand by the term units?”
Units are defined as the term that is used to express the standard amount of physical quantities and which are chosen to measure those physical quantities of the same kind.
These units are further divided into two parts:-
- Fundamental units
- Derived units
Classification of Units
The units are classified into derived and fundamental units.
Fundamental Unit: The units which are not derived from any other units are called the fundamental units. These types of units are already present in their simplest form and can not be resolved further. These are classified as the basic units of physical quantities.
Some of the fundamental units are: metre for measuring length, kilogram for measuring mass, seconds to measure time,kelvin to measure the temperature and ampere to measure current.
Derived Units: The units which are derived from the basic fundamental units are said to be derived units. These units are used to measure the physical quantities but the fact that these can be further resolved into simpler units or the fundamental units.
Some of the derived units are: metre per second to measure speed, kilogram per metre cube to measure density etc. are some of its examples.
There are a variety of physical quantities with which we have to deal in physics and thus they too have the derived units. Below is a list of derived units comprising a comprehensive detail.
A comprehensive list of derived units
PHYSICAL QUANTITY | UNIT IN WORDS | UNIT USED |
Area | Square metre | m2 |
Volume | Cubic Metre | m3 |
speed | Metre per second | m/s |
velocity | Metre per second | m/s |
acceleration | Metre per square second | m/s2 |
density | Kg per cubic metre | kg/m3 |
force | newton | m·kg·s-2 |
pressure | pascal | m-1·kg·s-2 |
stress | pascal | m-1·kg·s-2 |
work | joule | m2·kg·s-2 |
energy | joule | m2·kg·s-2 |
power | watt | m2·kg·s-3 |
frequency | Hz | s-1 |
voltage | volt | m2·kg·s-3·A-1 |
charge | coulomb | s·A |
resistance | ohm | m2·kg·s-3·A-2 |
impulse | Newton second | m⋅kg⋅s−1 |
momentum | Newton second | m⋅kg⋅s−1 |
Moment of inertia | Kilogram square metre | m2⋅kg |
Surface tension | Newton per meter | kg⋅s−2 |
Energy density | Joule per cubic meter | m−1⋅kg⋅s−2 |
capacitance | farad | A2 s4 kg−1 m−2 |
Magnetic flux | weber | m2·kg·s-2·A-1 |
Inductance | henry | m2·kg·s-2·A-2 |
Electric conductance | siemens | m-2·kg-1·s3·A2 |
Kinematic viscosity | Square metre per second | m2⋅s−1 |
Linear mass density | Kilogram per metre | m−1⋅kg |
Radiance | Watt per steradian cubic metre | kg⋅s−3 |
Fuel efficiency | Metre per cubic metre | m−2 |
Molarity | Mole per cubic metre | m−3⋅mol |
Molar volume | Cubic metre per mole | m3⋅mol−1 |
molality | Mole per kilogram | kg−1⋅mol |
Molar mass | Kilo gram per mole | kg⋅mol−1 |
Electric current density | Ampere per square metre | m−2⋅A |
Electric charge density | Coulamb per cubic metre | m−3⋅s⋅A |
Resistivity | Ohm metre | m3⋅kg⋅s−3⋅A−2 |
Magnetic dipole moment | Joule per tesla | m2⋅A |
Electron mobility | Square metre per volt second | kg−1⋅s2⋅A |
CONCLUSION
Every physical quantity needs to be expressed by any of the specific units. Therefore every physical quantity has its own unique unit be it made up of either a fundamental unit or a derived unit. Moreover, there are almost 7 basic fundamental base units who are the originators of derived units. Applying any kind of operations like multiplication, division, powers etc. leads to formation of these derived units.
Therefore the derived units are those types of units which lead to formation with the help of the basic fundamental units or the derived units are made by combining the base S.I. units. Also, the calculations implemented on these derived units always follow the similar procedure as the unit conversion calculations undergo.
