Fundamental units in physics are a set of base units used to define all other derived units of measurement; they are chosen by convention and cannot be expressed in terms of other units.
In the International System of Units (SI), there are seven fundamental units, each representing a different physical quantity. These units form the foundation upon which all other measurements are built.
The Seven Fundamental SI Units
The following table outlines the seven fundamental SI units:
| Quantity | Unit | Symbol | Definition |
|---|---|---|---|
| Length | meter | m | The length of the path travelled by light in vacuum during a time interval of 1/299,792,458 of a second. |
| Mass | kilogram | kg | The kilogram is defined by taking the fixed numerical value of the Planck constant h to be 6.62607015 × 10−34 when expressed in the units J s, which is equal to kg m2 s−1, where the meter and the second are defined in terms of c and ΔνCs. |
| Time | second | s | The duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom. |
| Electric Current | ampere | A | Defined by taking the fixed numerical value of the elementary electric charge e to be 1.602176634 × 10−19 when expressed in the unit C, which is equal to A s, where the second is defined in terms of ΔνCs. |
| Thermodynamic Temperature | kelvin | K | Defined by taking the fixed numerical value of the Boltzmann constant k to be 1.380649 × 10−23 when expressed in the unit J K−1, which is equal to kg m2 s−2 K−1, where the kilogram, meter and second are defined in terms of h, c and ΔνCs. |
| Amount of Substance | mole | mol | The amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon-12. When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles. |
| Luminous Intensity | candela | cd | The luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 × 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian. |
Significance of Fundamental Units
- Consistency: They provide a standardized system for measurement, ensuring consistency in scientific research and engineering applications worldwide.
- Derivation of Other Units: Derived units, such as the newton (force) or the joule (energy), are expressed as combinations of these fundamental units. For example, 1 Newton = 1 kg⋅m/s².
- Accuracy: The definitions of fundamental units are based on fundamental physical constants, providing high accuracy and stability.
- Communication: They facilitate clear and unambiguous communication of scientific and technical information.
In summary, fundamental units are the foundational building blocks of measurement in physics, providing a standardized and consistent basis for quantifying the physical world.
