Class 11 Physics Units and Measurements Units

Units

A unit is an internationally accepted standard for measurements of quantities.

  • Measurement consists of a numeric quantity along with a relevant unit.
  • Units for Fundamental or base quantities (like length, time etc.) are called Fundamental units.
  • Units which are combination of fundamental units are called Derived units.
  • Fundamental and Derived units together form a System of Units.
  • Internationally accepted system of units is SystèmeInternationale d’ Unites (French for International system of Units) or SI. It was developed and recommended by General Conference on Weights and Measures in 1971.
  • SI lists 7 base units as in the table below. Along with it, there are two units - radian or rad (unit for plane angle) and steradian or sr (unit for solid angle). They both are dimensionless.

Base Quantity

Name

Symbol

Length

metre

m

Mass

kilogram

kg

Time

second

s

Electric Current

ampere

A

Thermo dynamic Temperature

kelvin

K

Amount of Substance

mole

mol

Luminous intensity

candela

cd

 

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