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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
It is a well known fact that during a total solar eclipse the disk of the moon almost completely covers the disk of the Sun. From this fact and from the information you can gather from examples 2.3 and 2.4, determine the approximate diameter of the moon.

Distance of the Moon from the Earth = 3.84 × 108 m 

Distance of the Sun from the Earth = 1.496 × 1011 m 


Diameter of the Sun = 1.39 × 109 m 

During a lunar eclipse, the position of the sun, moon and earth is as shown below:



Here comma space

increment TRS space and space increment TPQ space are space similar. space

So comma space space PQ over RS space equals space VT over UT space

straight i. straight e. comma space fraction numerator 1.39 space cross times space 10 to the power of 9 over denominator RS end fraction space equals space fraction numerator 1.496 space cross times space 10 to the power of 11 over denominator 3.84 space cross times space 10 to the power of 8 end fraction space

rightwards double arrow space RS space equals space left parenthesis 1.39 space 3.84 space cross times space 10 to the power of 8 right parenthesis space cross times space 10 to the power of 6 space

space space space space space space space space space space space space equals space 3.57 space cross times space 10 to the power of 6 space

Therefore comma space space space 3.57 space cross times space 10 to the power of 6 space space is space the space diameter space of space the space moon. space


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Give four examples of physical quantities.

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

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

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. 
825 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.


878 Views