Units and Measurement

Physics Part I

Physics

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A great physicist of this century (P.A.M. Dirac) loved playing with numerical values of

Fundamental constants of nature. This led him to an interesting observation. DiracÂ found that from the basic constants of atomic physics (*c*, *e*, mass of electron, mass ofÂ proton) and the gravitational constant *G*, he could arrive at a number with theÂ dimension of time. Further, it was a very large number, its magnitude being close toÂ the present estimate on the age of the universe (~15 billion years). From the table ofÂ fundamental constants in this book, try to see if you too can construct this number(or any other interesting number you can think of ). If its coincidence with the age of

the universe were significant, what would this imply for the constancy of fundamental

constant.Â

Fundamental constants of nature. This led him to an interesting observation. DiracÂ found that from the basic constants of atomic physics (

the universe were significant, what would this imply for the constancy of fundamental

constant.Â

Putting these values in the above equation, we get

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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?

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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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Give four examples of physical quantities.

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

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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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