Units and measurements , Physical Quantities

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Units and measurements
Units and measurements
♦ Physical Quantity
• The quantities which can be measured by an instrument or anything which can be expressed in terms of numbers which describes the laws of Physical World, known as Physical Quantity.• For example, the physical quantity ‘Time’ can be quantified as ns, where n is the numerical value and s (second) is the unit.

• A physical quantity possesses at least two characteristics in common….. namely
1. The numerical magnitude / Numeric Value
2. Unit in which it is measured.

• There are two main types of physical quantity, they are ……
1. Fundamental or basic quantity
2. Derived quantity

◘ On the basis of direction and their magnitude there are other types of physical quantity include the vector quantity and scalar quantity.

Note :-
• Beside Fundamental or basic quantity and Derived quantity there are another types of quantity which are nither fundamental nor derived. These quantities are called Supplementary quantities.
Example :- Plane angles and Soild angles

♦ Fundamental or Base Quantities
• Those physical quantities which are independent in nature or rather we can say they do not depend on other physical quantities are known as fundamental or base physical quantities.• Example :-Length, Electric Current, Mass, Time, Temperature, Luminous intensity.
♦ Derived Quantities
All the physical quantities which are not the base quantities or fundamental quantities but are depend upon the fundamental quantities are known as derived quantities.• Derived quantities cannot be measured directly. They can only be computed. As because they are derived from two or more than two fundamental quantities.

Example :- Density, Force, Pressure Area, Velocity etc.

• For an example the derived quantitites Velcity derived from two fundamental unit or base unit namely ..
1. Distance
2. Time

• Velocity = Distance / Time

♦ Supplementary Quantity
• There are also two physical quantities which are neither fundamental nor derived. These quantities are called supplementary quantities• Example :- Plane angles and Soild angles
Types of Physical Quantities
Types of Physical Quantities
List of the Seven Fundamental Quantities
S.No. Fundamental Quantity SI Unit
1. Length Metre (M)
2. Mass Kg
3. Time Second (s)
4. Current Ampere (A)
5. Temperature Kelvin
6. Luminous Intensity Candela
7. Amount of substance Mole


Two Supplementary Quantity
8. Plane angle Radian
9. Soild angle Steradian


List of some Derived Quantities
S.No Quantity Formula SI Unit
1. Magnetic Field Force / (Electric Current x Displacement) N amp-1m– 1
or Tesla or Weber / m2
2. Density Mass/Volume kgm– 3
3. Area of Rectangle Length x Breadth m2
4. Velocity Distance / Time ms – 1
5. Area of Square (side)2 m2
6. Accleration Change in Velocity / Time ms-2
7. Area of Triangle 1/2 x Base x Height m2
8. Force Mass x Acceleration N
9. Work Force x Distance N.m or Jule
10 Pressure Force / Area N/m2, or kg·m−1 s −2
11 Linear momentum Mass x Velocity kg·m−1
12 Volume of Cuboid Length x Breadth x Height m3

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