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Units and Measurement

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Physics Part I

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Physics

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The nearest star to our solar system is 4.29 light years away. How much is this distance in terms of parsecs? How much parallax would this star (named AlphaCentauri) show when viewed from two locations of the Earth six months apart in its orbit around the Sun ?


Distance space of space the space star space from space the space solar space system space equals space 4.29 space ly

1 space light space year space equals space Speed space of space light space cross times space 1 space year

space space space space space space space space space space space space space space space space space space space space space equals space 3 space cross times space 10 to the power of 8 space cross times space 365 space cross times space 24 space cross times space 60 space cross times space 60 space

space space space space space space space space space space space space space space space space space space space space equals space 94608 space cross times space 10 to the power of 11 space straight m space

therefore space 4.29 space ly space equals space 405868.32 space cross times space 10 to the power of 11 space straight m
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 left square bracket space 1 space parsec space equals space 3.08 cross times 10 to the power of 16 space straight m right square bracket space

therefore space 4.29 space ly space equals fraction numerator 405868.32 space cross times space 10 to the power of 11 space straight m over denominator space 3.08 cross times 10 to the power of 16 space straight m end fraction space equals space 1.32 space parsec

Now comma space using space the space formula comma space

straight theta space equals space straight d over straight D space
where comma space

straight d space equals space diameter space of space Earth apostrophe straight s space orbit space equals space 3 cross times 10 to the power of 11 space straight m

straight D space equals space Distance space of space star space from space the space Earth space equals 405868.32 space cross times space 10 to the power of 11 space end exponent straight m

therefore space straight theta space equals space fraction numerator 3 cross times 10 to the power of 11 space straight m over denominator 405868.32 space cross times space 10 to the power of 11 space end exponent straight m end fraction

space space space space space space space space equals space 7.39 space cross times space 10 to the power of negative 6 space end exponent rad space

But comma space 1 space sec space equals space 4.85 space cross times space 10 to the power of – 6 end exponent space rad

therefore space space 7.39 space cross times space 10 to the power of negative 6 space end exponent rad space space equals space fraction numerator 7.39 space cross times space 10 to the power of negative 6 space end exponent over denominator space 4.85 space cross times space 10 to the power of – 6 end exponent space end fraction space equals space 1.52 space "
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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. 
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