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CBSE  CLASS XI PHYSICS  UNIT -1  PHYSICAL WORLD AND MEASUREMENT CHAPTER-2  UNITS AND MEASUREMENT Physical Quantities: The quantities which can be measured directly or indirectly is known as physical quantities. e g : Mass , Length , Time etc. Unit: Unit is the standard by which we can compare the physical quantities. e g : Kilogram, meter, second etc. Magnitude of a quantity Q = numerical value x size of its unit. Q=nu Now Q= n 1 u 1 = n 2 u 2. If u 1 >u 2 , then n 1 <n 2 i.e. a bigger unit has smaller numerical value and   vice-versa. e g     Length of a road is =   3 m = 300 cm Fundamental quantities: The quantities which are basic and cannot derived from other quantities are called fundamental or basic physical quantities. e g mass , length ,time . Fundamental Units: The units of measurement of all fundamental quantities are called fundamental units. e g mass- kilogram .   S N Basic Physical Quantities Fundamental