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Units and Measurement

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Physics Part I

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Physics

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CBSE Gujarat Board Haryana Board

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Class 10 Class 12

Just as precise measurements are necessary in science, it is equally important to be able to make rough estimates of quantities using rudimentary ideas and common observations. Think of ways by which you can estimate the following (where an estimate is difficult to obtain, try to get an upper bound on the quantity):
(d) the number of strands of hair on your head


Area of the head surface carrying hair = A

Radius of hair strand can be measured using a screw gauge. 

Let radius of the hair strand be 'r'. 


Area space of space 1 space hair space equals space πr squared space

No. space of space strands space of space hair space equals space fraction numerator Total space surface space area over denominator Area space of space one space hair space end fraction space
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals space fraction numerator straight A over denominator space πr squared space end fraction
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Define unit.

The quantity used as a standard of measurement is called unit. 

Example: Unit of time is second. 

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Give four examples of physical quantities.

Examples of Physical quantitie are force, mass, density and power.
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What is the need of measurement?

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 is measurement?

Measurement is the process of attaching a numeric value to an aspect of a natural phenomenon. Measurement is making the quantitative knowledge of a physical quantity. 
1289 Views

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.


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