MEASUREMENT

                                                     


                Measurement is the comparison between unknown quantities with known standard quantities.

  • Some of the importance of measurement are:

  1. Measurement is important for selling and buying goods in markets.

  2. It is essential for doing chemical experiments.

  3. It is necessary for doing new inventions.

  4. It is important for making laws and rules.

  • Physical quantities are those quantities which can be measured and are countable. For example: height, weight, length, etc.

  • Non-physical quantities are those quantities which cannot be measured and are not countable. For example: love, emotion, anger, sadness, happiness, etc.

  • There are two types of physical quantities. they are

  1. Fundamental quantities

  2. Derived quantities 

  • Fundamental quantities are those quantities which are not dependent upon any other quantities and are independent.


FUNDAMENTAL QUANTITIES

UNITS

SYMBOL

Length 


Meter

m

Mass

Kilogram

kg

Time

Second

s

Temperature

Kelvin

K

Luminous intensity

Candela

cd

Current 

Ampere

A

Amount of substance

mole

mol 


  • Derived quantities are those quantities which are dependent on fundamental quantities.


Derived quantities

Units 

Area

m2

Volume

m3

Density

Kg/m3

Speed / velocity

m/s

Acceleration

m/s2

Force

Newton 

Momentum

Kg m /s

Moment of force

Newton meter

Work/ energy

Joule 

Power

Watt 

pressure

Pascal 

Frequency

hertz

Potential difference

volt

Electric resistance

Ohm 

Electric charge

coulomb


  • The comparison with standard quantity of the same kind with unknown physical quantity is known as unit.

  • There are 4 systems of units. They are :

  1. F.P.S system 

  • F.P.S system is also known as British system of unit. In this system of unit length, mass and time are measured in foot, pound and second respectively.

  1. C.G.S system

  • C.G.S system is the system of units in which length, mass and time are measured in centimetre, gram and second respectively.

  1. M. k. S system

  • M.K.S is the system of unit in which length, mass and time are measures in meter, kilogram and second respectively. 

  1. SI system

  • SI system is the modified form of MKS system and also known as rationalized system.

  • Some of the advantages of SI system are:

  1. It explains fundamental quantities for measurement of physical quantities.

  2. It makes uniformity in measurement all over the world.

  • Rules of writing units are:

  1. The symbol for a unit which is not named in honor of scientist is written in small letter. 

  2. The symbol for a unit which is named in honor of scientist is written in initial letter. 

  3. A unit in short form is never written in plural.

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