Question

In which year the SI system of units was developed and recommended by the general conference on weights and measures?
A) $$1951$$
B) $$1961$$
C) $$1971$$
D) $$1981$$

Answer 1

Hint:SI unit is an abbreviation of the French word System International. The International System of Units (SI) is the metric system that is universally accepted as a standard for measurements.

Complete step by step solution:
The SI system of units was developed and recommended by the General Conference on Weights and Measures in$$1971$$.
SI units have an important contribution in scientific and technological research and development. It comprises $$7$$ base units which are used for defining $$22$$ derived units.
The basic $$7$$ fundamental units for fundamental quantities are as following,
Physical Quantities
S.I. Unit
For Mass is Kilogram ($$kg$$)
For Length is Meter ($$m$$)
For Time is Second ($$s$$)
For Electric current is Ampere ($$A$$)
For Temperature is Kelvin ($$K$$)
For Amount of substance is Mole ($$mol$$)
For Luminous intensity is Candela ($$cd$$)

Unit of length, meter ($$m$$): Meter is the SI unit of length and is defined by taking the fixed value of the speed of light in vacuum. It is expressed as $$m{s}^{-1}$$.

Unit of mass, kilogram ($$kg$$): Kilogram is the SI unit of mass and is defined by taking the fixed value of the Planck constant. It is expressed as $$kg{m}^2.s^{-1}$$.

Unit of time, second ($$s$$): Second is the SI unit of time and is defined by taking the fixed value of Cesium frequency. It is expressed as $$s^1$$.

Unit of electric current, ampere ($$A$$): Ampere is the SI unit of electric current and 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 and is defined by taking the fixed value of Boltzmann constant $$k=1.380649\times {10}^{-23}$$.

Unit of the amount of substance, mole ($$mol$$): Mole is the SI unit of amount of substance and is defined by the fixed value of Avogadro constant $$N_A$$. One mole contains $$6.02214076\times {10}^{23}$$ elementary entities and is expressed as $$mo{l}^{-1}$$.

Unit of luminous intensity, candela ($$cd$$): Candela is the SI unit of luminous intensity and is defined by the fixed value of the luminous efficacy.

Note: The fundamental units are independent of any other units including themselves.
There are a total of seven fundamental units in the SI unit system.
The derived units are those units which are obtained by mathematical operations of fundamental units.