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Units and Measurement

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Physics Part I

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CBSE Gujarat Board Haryana Board

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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


Give four examples of physical quantities.

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

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. 

Define unit.

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

Example: Unit of time is second. 


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. 

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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