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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
The farthest objects in our Universe discovered by modern astronomers are so distant  that light emitted by them takes billions of years to reach the Earth. These objects (known as quasars) have many puzzling features, which have not yet been satisfactorily explained. What is the distance in km of a quasar from which light takes 3.0 billion years to reach us?

We have here, 

Time taken by quasar light to reach Earth = 3 billion years 

straight t space equals space 3.0 space cross times space 10 to the power of 9 space years space
space space equals 3.0 space cross times space 10 to the power of 9 space cross times 365 cross times 24 cross times 60 cross times 60 space straight s
space space equals space 9.46 space cross times space 10 to the power of 16 space straight s space

Speed space of space light space equals space 3 space cross times space 10 to the power of 8 space straight m divided by straight s

Distance space between space Earth space and space quasar space is comma space

equals space left parenthesis 3 space cross times space 10 to the power of 8 right parenthesis space cross times space 9.46 space cross times space 10 to the power of 16 space straight s space

equals space 283824 space cross times space 1020 space straight m space

equals space 2.8 space cross times space 10 to the power of 22 space km

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Give four examples of physical quantities.

Examples of Physical quantitie are force, mass, density and power.
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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.


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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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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

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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