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Units and Measurement

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Physics Part I

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Class 10 Class 12
State the number of significant figures in the following :
a) 0.007 m2

b) 2.64 1024kg
(c) 0.2370 g cm–3
(d) 6.320 J 
(e) 6.032 N m
(f) 0.0006032 m2

a) 1

The given quantity is 0.007 m2

If the number is less than one, then all zeros on the right of the decimal point (but left to the first non-zero) are insignificant. This means that here, two zeros after the decimal are not significant. Hence, only 7 is a significant figure in this quantity. 

b) 3 

Here, the power of 10 is irrelevant for the determination of significant figures. Hence, all the digits are significant figures.

c) 4 

d) 4

e) 4

f) 4


Define unit.

The quantity used as a standard of measurement is called unit. 

Example: Unit of time is second. 


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.


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. 

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. 

Give four examples of physical quantities.

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