Standard Units of measurement in Physics pdf download

What is a Physics?

Physics is the study of nature and its laws. The word physics has been derived from a Greek word physis which means nature. Physics is one of the oldest academic disciplines, perhaps the oldest through its inclusion of astronomy.


The chosen standard used for measuring a physical quantity is called unit. Unit should be :

  1. well defined
  2. easy to reproduce
  3. easy to compare
  4. internationally accepted
  5. independent of changes in physical conditions

Types of Units 

Units are of two types : 1. Fundamental Unit and 2. Derived Unit

Units depend on choice. Each choice of units leads to a new system (set) of units. The internationally accepted systems are 1. CGS system,2. MKS System, 3. FPS System,4. SI Units.

Fundamental Unit

Standard Units

Measurement of any physical quantity involves comparison with a certain basic arbitrarily chosen and widely accepted reference standard called unit.

SI System

It is based on the following seven basic/fundamental  units and two supplementary units.

Basic/ Fundamental Units

Physical Quantity SI Unit Symbol
Length metre m
Mass kilogram kg
Time second s
Electric current ampere A
Thermodynamic Temperature kelvin K
Luminous intensity candela Cd
Amount of substance mole mol

Supplementary Units

Physical Quantity Name of Units Symbol
Plane angle radian rad
solid angle steradian sr

Derived Units

Physical Quantity cgs units SI Unit Relation
Force dyne newton 1 newton = 105 dyne
Work erg joule 1 joule = 107 erg

Greatest Units

Length Units

What is light year?

It is a distance travelled by light in one year in vacuum.

Name Measure
1 light year 9.46 × 1015 m
1 parsec 3.084 × 1016 m = 3.26 ly
1 Astronomical Unit (A.U) 1.5 × 1011 m
1 Nautical mile or Seamile
6020 ft.
1 Micron 1 µm = 10-6 m
1 Angstron (Å) 10-10 m

Mass Units

Name Measure
1 Metric ton 103 kg
1 Quintal 102 kg
1 Atomic Mass Unit (amu) or Dalton 1.66 × 10-27 kg
1 Slug 14.59 kg
1 Pound
0.4537 kg
1 Chandrashekhar limit 1.4 times the mass of sun = 2.8 × 1030 kg

Time Units

Name Mesaure
1 Solar day 86400 sec.
1 Year 365½ solar days
1 Lunar month 27.3 solar days
Tropical year It is the year in which total solar eclipse occurs.
Leap Year It is the year in which the month of February is of 29 days.

 Prefix Used In Metric System

Prefix Symbol Multiplier
deci d 10-1
centi c 10-2
milli m 10-3
micro µ 10-6
nano n 10-9
pico p 10-12
femto f 10-15
atto a 10-18
zepto z 10-21
yocto y 10-24
deca da 101
hecto h 102
kilo k 103
mega M 106
giga G 109
tera T 1012
peta P 1015
exa E 1018
zetta Z 1021
yotta Y 1024

If anybody have still any doubt, please comment below in box

All the best for your upcoming exam!

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