Thus s.i. units are based on seven fundamental units or base units and two suppementary units.
table of s.i base units
sr.no. physical quantity name of abbreviations for s.i.
s.i.unit units (symbols)
1. length meter m
2. mass kilogram kg
3. time second s
4. electric current ampere A
5. luminous intensity candela Cd
6. thermodynamic temperature kelvin K(not°k)
7. amount of substance mole mol
. table os supplementary s.i units
sr.no. quantity name of s.i.unit symbol
1. plane angle radian red
2. solid angle steradian sr
These seven fundamental or base units and two spplementary units can be defined as:
Base units or fundamental units:
(i) The metre (m) as the unit of length.
A metre is equal to 1,650,763.73 wavelengths in vacuum of orange light (radiations) emitted by an isotope of krypton-86.
(ii) The kilogram (kg) as unit of mass.
A kilogram is equal to the mass of platinum-irridium alloy cylinder of diameter equal to its height. It is kept at the international bureau of weights and measures at severs near paris.
(iii) the second (s) as the unit of time.
A second is the duration of 9,192,631,770 vibrations of the radiations emitted by ground state of the ceasium-133 atom.
(iv) The ampere (A) as the unit of electric current.
An ampere is that constant current which when flowing through two straight parallel conductors of infinite length and negligible area of cross section and placed one metre apart in vacuum would repel or attract each other with a force equal to 2*10or-7 newton per metre length of the conductors.
(v) The kelvin (k) as the unit of temperature.
The kelvin is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water.
(vi) The candela (Cd) as the unit of luminous intensity.
The candelea is the luminous intensity in the perpendicular direction of a surface of 1/600,000 square metre of a black body at the temperature of freezing platinum under a pressure of 101325 N/m or2.
(vii) the mole (mol) as the unit for quantity of matter or amount of substance.
A mole is the amount of a substance which contains as many elementary units as there are carbon atoms in exactly 0.012 kg of c12.
Supplementary units : (i) The radian (red) as the unit of plane angle.
A radian is the angle subtended at the centre of a circle (between two radii) by an arc of the circle of length equal to radius of the circle.
Plane angle in radian (0)= length of arc (1)/radius of circle(r).
(ii) The steradian (sr) as the unit of solid angle.
A steradian is a solid angle subtended at the centre of a sphere by an area of the surface of the sphere,equal to that of a square whose each side is equal to the radius of the sphere.
solid angle in steradian = area cut out from the surface of sphere/(radius)or2
table of s.i base units
sr.no. physical quantity name of abbreviations for s.i.
s.i.unit units (symbols)
1. length meter m
2. mass kilogram kg
3. time second s
4. electric current ampere A
5. luminous intensity candela Cd
6. thermodynamic temperature kelvin K(not°k)
7. amount of substance mole mol
. table os supplementary s.i units
sr.no. quantity name of s.i.unit symbol
1. plane angle radian red
2. solid angle steradian sr
These seven fundamental or base units and two spplementary units can be defined as:
Base units or fundamental units:
(i) The metre (m) as the unit of length.
A metre is equal to 1,650,763.73 wavelengths in vacuum of orange light (radiations) emitted by an isotope of krypton-86.
(ii) The kilogram (kg) as unit of mass.
A kilogram is equal to the mass of platinum-irridium alloy cylinder of diameter equal to its height. It is kept at the international bureau of weights and measures at severs near paris.
(iii) the second (s) as the unit of time.
A second is the duration of 9,192,631,770 vibrations of the radiations emitted by ground state of the ceasium-133 atom.
(iv) The ampere (A) as the unit of electric current.
An ampere is that constant current which when flowing through two straight parallel conductors of infinite length and negligible area of cross section and placed one metre apart in vacuum would repel or attract each other with a force equal to 2*10or-7 newton per metre length of the conductors.
(v) The kelvin (k) as the unit of temperature.
The kelvin is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water.
(vi) The candela (Cd) as the unit of luminous intensity.
The candelea is the luminous intensity in the perpendicular direction of a surface of 1/600,000 square metre of a black body at the temperature of freezing platinum under a pressure of 101325 N/m or2.
(vii) the mole (mol) as the unit for quantity of matter or amount of substance.
A mole is the amount of a substance which contains as many elementary units as there are carbon atoms in exactly 0.012 kg of c12.
Supplementary units : (i) The radian (red) as the unit of plane angle.
A radian is the angle subtended at the centre of a circle (between two radii) by an arc of the circle of length equal to radius of the circle.
Plane angle in radian (0)= length of arc (1)/radius of circle(r).
(ii) The steradian (sr) as the unit of solid angle.
A steradian is a solid angle subtended at the centre of a sphere by an area of the surface of the sphere,equal to that of a square whose each side is equal to the radius of the sphere.
solid angle in steradian = area cut out from the surface of sphere/(radius)or2