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Units and Measurement

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Physics Part I

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Physics

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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) :
(a) the total mass of rain-bearing clouds over India during the Monsoon.


straight A space Metrologist space records space about space 215 space cm space of space rainfall space in space India

space straight i. straight e. comma space the space height space of space water space column comma space straight h space equals space 215 space cm space equals space 2.15 space straight m

Ares space of space country comma space straight A space equals space 3.3 space cross times space 10 to the power of 12 space straight m squared

So comma space

Volume space of space rain space water comma space straight V space equals space straight A cross times space straight h 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 space space space space space equals space 7.09 space cross times space 10 to the power of 12 space end exponent straight m cubed space

Density space of space water comma space straight rho space equals space 1 space cross times space 10 to the power of 3 space end exponent kg space straight m to the power of – 3 end exponent

Therefore comma space

Mass space of space rain space water equals straight rho space cross times space straight V space equals space 7.09 space cross times space 10 to the power of 15 space end exponent kg space

Hence comma space total space mass space of space rain space bearing
space clouds space over space India space equals space space 7.09 space cross times space 10 to the power of 15 space end exponent kg space
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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. 

1172 Views

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

Give four examples of physical quantities.

Examples of Physical quantitie are force, mass, density and power.
821 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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