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Physical quantities are of two basic types: derived quantities and fundamental quantities. Fundamental quantities are the ones that are represented independently and are not defined in terms of other physical quantities. There are seven fundamental quantities and some examples are – length, time, temperature, electric current, and so on.
While derived quantities are defined as those physical quantities that can be represented in the form of other fundamental quantities. So all the quantities other than the seven fundamental quantities are derived. Examples of derived quantities are force, acceleration etc.
Measurement system
In order to measure various units there is a system known as the system of units. There are four systems of units these are –
Cgs system- this system is set up at France which consists of centimetre , gram and second are the units of length, weight and time.
Fps system – It is a British system with foot, pound, and second as the fundamental units of length, mass and time.
Mks system – it is a French system and the fundamental units are metre, kilogram and second.
SI : It stands for the International system of units.SI is the abbreviation for “Systeme Internationale d’ United “.It is the modernized form of the MKS system.It was adopted by the eleventh General Conference of weights and measures. It is based on seven basic units and two supplementary units.
Dimensions of a physical quantity
Dimensions for a given physical quantity is the power or the exponents to which the seven fundamental quantities are raised.
For example, Density is defined as mass per unit volume.So it can be written as follows -:
Density = Mass ÷ volume
Here mass has a dimension of M and volume as L3.So the SI unit dimensional formula is ML3.
Coefficient of viscosity
The formula for Coefficient of viscosity is force x distance /area x velocity
Therefore we can write it as [MLT-2] for force, [L] for distance, [L2] for the area and
[LT-1] for velocity. On further simplification, we get the dimensions as [ML-1T-1] .
Dimensional formula
A Dimensional formula is defined as the expression which shows the exponent or the powers to which a given physical quantity is raised.
Seven Basic dimensions
Dimensions are always denoted in a square bracket []
Dimensional formula for some physical quantities
Conclusion
In physics there are physical quantities which are of – Fundamental and derived quantities. The various systems that are used for measurement are the Cgs system, mks system,fps system, and the SI system. further dimensions are defined as the power or the exponents to which the seven fundamental quantities are raised and the dimensional formula is the expression that represents the physical quantities. The dimensional formula thus gives the idea regarding what the fundamental quantities are for a given physical quantity. There are a total of seven dimensions based on the seven fundamental quantities. These dimensions are also called the dimensions of the world. They are represented in square brackets. The dimensions of length for example is [L] and for luminous intensity [cd]
