To get the complete knowledge of any physical quantity, measurement is needed. Measurement of any physical quantity involves comparison with a certain basic, arbitrarily chosen, internationally accepted reference standard called unit. Knowledge without measurement is incomplete and unsatisfactory.
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What are the two main required characteristics of a unit?
Characteristics of unit are:
1. Invariability 2. Avaialbility
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Define physical quantity.
A measurable quantity in terms of which laws of Physics can be expressed is called physical quantity.
The result of a measurement of a physical quantity is expressed by a number accompanied by a unit.