ï»¿ The farthest objects in our Universe discovered by modern astronomers are so distant Â that light emitted by them takes billions of years to reach the Earth. These objectsÂ (known as quasars) have many puzzling features, which have not yet been satisfactorilyÂ explained. What is the distance in km of a quasar from which light takes 3.0 billionÂ years to reach us? from Physics Units and Measurement Class 11 Manipur Board

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

We have here,Â

Time takenÂ by quasar light to reach Earth = 3 billion yearsÂ

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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.
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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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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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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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