Revision Notes for Class 11 Physics
Chapter 1 – Units and Measurements
Units:
A unit can be defined as an internationally accepted standard for measuring quantities.
• Measurement has been included in a numeric quantity along with a specific unit.
• The units in the case of base quantities (such as length, mass etc.) are defined as
Fundamental units.
• Derived units are the units that are the combination of fundamental units.
• Fundamental and Derived units constitute together as a System of Units.
• An internationally accepted system of units can be defined as Système Internationale
d’ Unites (This is how the International System of Units is represented in French) or
SI. In 1971, it was produced and recommended by General Conference on Weights
and Measures.
• The table shown below is the list of 7 base units mentioned by SI.
There are two units along with it. They are, radian or rad (unit for plane angle) and steradian
or sr (unit for solid angle). Both of these are dimensionless.
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,Base Quantity Name Symbol
Length metre m
Mass kilogram kg
Time second s
Electric Current ampere A
Thermodynamic
kelvin K
Temperature
Amount of Substance mole mol
Luminous intensity candela cd
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, Significant Figures
Every measurement gives us an output in a number that includes reliable digits and uncertain
digits.
Reliable digits added with the first uncertain digit can be defined as significant digits or
significant figures. This represents the precision of measurement which is dependent on the
least count of instruments used for measurement.
The period of oscillation of a pendulum is 1.62 s can be taken as an example. Here 1 and 6
will be reliable and 2 is uncertain. Hence, the measured value will have three significant
figures.
Rules for the determination of the number of significant figures
• All non-zero digits will be significant.
• Irrespective of the decimal place, all zeros between two non-zero digits will be
significant irrespective of the decimal place.
www.vedantu.com 3
Chapter 1 – Units and Measurements
Units:
A unit can be defined as an internationally accepted standard for measuring quantities.
• Measurement has been included in a numeric quantity along with a specific unit.
• The units in the case of base quantities (such as length, mass etc.) are defined as
Fundamental units.
• Derived units are the units that are the combination of fundamental units.
• Fundamental and Derived units constitute together as a System of Units.
• An internationally accepted system of units can be defined as Système Internationale
d’ Unites (This is how the International System of Units is represented in French) or
SI. In 1971, it was produced and recommended by General Conference on Weights
and Measures.
• The table shown below is the list of 7 base units mentioned by SI.
There are two units along with it. They are, radian or rad (unit for plane angle) and steradian
or sr (unit for solid angle). Both of these are dimensionless.
www.vedantu.com 1
,Base Quantity Name Symbol
Length metre m
Mass kilogram kg
Time second s
Electric Current ampere A
Thermodynamic
kelvin K
Temperature
Amount of Substance mole mol
Luminous intensity candela cd
www.vedantu.com 2
, Significant Figures
Every measurement gives us an output in a number that includes reliable digits and uncertain
digits.
Reliable digits added with the first uncertain digit can be defined as significant digits or
significant figures. This represents the precision of measurement which is dependent on the
least count of instruments used for measurement.
The period of oscillation of a pendulum is 1.62 s can be taken as an example. Here 1 and 6
will be reliable and 2 is uncertain. Hence, the measured value will have three significant
figures.
Rules for the determination of the number of significant figures
• All non-zero digits will be significant.
• Irrespective of the decimal place, all zeros between two non-zero digits will be
significant irrespective of the decimal place.
www.vedantu.com 3
