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PHYSICS All measurement quantities, their base si units, and symbols
QUANTITY  SYMBOL  Base SI UNIT  SYMBOL 
Length  L  meter  m 
Mass  M  kilogram  k 
Time  T  second  s 
Work  W  joule (m^{2}kg.s^{2)}  ^{J} 
Energy  E  joule (m^{2}kg.s^{2)}  J 
Electric Current  i  ampere  A 
Temperature  T  kelvin  K 
Intensity of flame  I_{v}  candela  cd 
Luminous intensity  I_{v}  candela  cd 
Plane Angle  ∅  radian  rad 
Solid Angle  ω  steradian  sr 
Force  F  newton  N 
Area  A  square meter  m^{2} 
Volume  V  Cubic meter  m^{3} 
Speed  v  meter per second  ms^{1} 
Angular velocity  ω  radian per second  rad s^{1} 
Frequency  f  Hertz  Hz 
Moment of Intertia  I  kilogram square meter  kgm^{2} 
Momentum  p  kilogram meter per second  kg ms^{1} 
Impulse  J  newton second  Ns 
Angular Momentum  L  kilogram square meter per second  kg m^{2}s^{1} 
Pressure  p  pascal  Pa 
Power  P  watt  W 
Surface tension  σ (lower case sigma)  newton per meter  Nm^{1} 
Viscosity  µ, η  newton second per square meter  N.s.m^{2} 
Thermal Conductivity  κ, λ, K  watt per meter per degree celcius  Wm^{1}C^{1} 
Specific Heat Capacity  c  joule per kilogram per Kelvin  j kg^{1}K^{1} 
Electric Charge  q  coulomb  C 
Potential Difference  ΔV  volt  V 
Electric Resistance  R  ohm  Ω 
Electric Capacity  c  farad  F 
Magnetic Induction  B  henry  H 
Magnetic Flux  Φ  weber  Wb 
Luminous Flux  Φ_{v}  lumen  lm 
Photometric power  Φ_{v}  lumen  lm 
Intensity of illumination  l_{x}  lux  lx 
Wavelength  λ  angstrom  A° 
Astronomical distance  au, AU  light year  ly 
Density  ρ  kilogram per meter square  kg.m^{3} 
Torque  τ  Newton meter  N 
Dynamic viscosity  η (eta)  pascal second  pa.s 
Acoustic pressure  L_{pa}  pascal (kg m^{1}s^{2})  pa 
Magnetic field strength  H  ampere per meter  A/m 
Quantity of electricity  C  coulomb (ampere second)  A.s 
Radioactivity  ☢  becquerel (s^{1})  bq 
Magnetic field intensity  B  tesla (Wbm^{2})^{}  T 
A physical unit is the chosen standard used for measuring a physical quantity. it should be:
 Well defined
 easy to reproduce
 easy to compare
 internationally accepted
 independent of changes in physical conditions
there are the following internationally accepted systems for measuring the units:
SYSTEM  FULL FORM 
CGS  CENTIMETREGRAMSECOND 
MKS  METREKILOGRAMMESECOND 
FPS  FOOTPOUNDSECOND 
Base SI UNITS  STANDARD INTERNATIONAL UNITS 
 fundamental units
 derived units
FUNDAMENTAL UNITS
Definition of fundamental units: Fundamental units are those fundamental quantities of measurement, from which every other physical quantity can be generated or derived. these are not dependent on any other units and are defined by the INTERNATIONAL SYSTEM OF UNITS. for example, meter, second, kilogram.
in base SI units, there are seven fundamental units given below:
PHYSICAL QUANTITY  SYMBOL  BASE SI UNIT 
LENGTH  m  METRE 
MASS  kg  KILOGRAM 
TIME  s  SECOND 
ELECTRIC CURRENT  A  AMPERE 
TEMPERATURE  K  KELVIN 
LUMINOUS INTENSITY  Cd  CANDELA 
AMOUNT OF SUBSTANCE  mol  MOLE 
besides these seven fundamental units, there are two supplementary units are also defined:
 radian [red]
 steradian (sr)

radian  Simply, it is a unit of measurement for plane angles that is based on the radius of a circle.

steradian  it is used to measure solid angles i.e. angle of a sphere that is subtended by a portion of the surface having an area equal to the square of the radius of that sphere.
Radian  to measure a plane angle
Steradian to measure a solid angle
 PLANE ANGLE 
a plane angle ∅ made up of the lines from two points meeting at a vertex(is a point where two or more curves, lines, or edges meet.), is defined by the arc length of a circle subtended by the lines and by the radius of that circle.
 SOLID ANGLE 
a solid angle ϖ made up of all the lines from a closed curve meeting at a vertex, it is defined by the surface area of a sphere which is subtended by the lines and the radius of that sphere.
Note: all the units which are defined in terms of fundamental units are called DERIVED UNITS.
following are the derived units and relation between SI and CGS units:
PHYSICAL QUANTITY  CGS UNITS  Base SI UNITS  RELATION 
Force  dyne  newton  1 newton=10^{5} dyne 
work  erg  joule  1 joule=10^{7} erg 
following are some practical units of length, mass, and time:
LENGTH  MASS  TIME 
light year = distance traveled by light in one year in vacuum.  1 Atomic mass unit (AMU) or Dalton = 1.66×10^{27} kg  Leap year = it is the year in which the month of February is of 29 days. 
1 lightyear = 9.46×10^{15}m  1 Metric ton = 10^{3} kg  1 Solar day = 86400 sec. 
1 Astronomical unit (A.U.)=1.5×10^{11}m  1 Quintol = 10^{2} kg  1 year = 365½ solar days 
1 Parsec = 3.26 lightyear i.e. 3.08×10^{16}m  1 Slug = 14.59 kg  1 Lunar month = 27.3 solar days. 
1 nautical mile or seamile = 6020 ft.  1 pound = 0.4537 kg  Tropical year = it is the year in which total solar eclipse occurs. 
1 Micron = 1µm i.e. 10^{6}m  1 Chandrashekar limit = 1.4 times the mass of sun i.e. 2.8×10^{30} kg  
1 Angstron (Å) =10^{10}m 
prefixes used in the metric system:
PREFIX  SYMBOL  VALUE 
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  10^{1} 
hecto  h  10^{2} 
kilo  k  10^{3} 
mega  M  10^{6} 
giga  G  10^{9} 
tera  T  10^{12} 
Peta  P  10^{15} 
exa  E  10^{18} 
Zetta  Z  10^{21} 
yotta  Y  10^{24} 
Conversion of units from one system to another system:
1 Inch  2.54 centimeter 
1 Foot  0.3 meter 
1 yard  0.91 meter 
1 Mile  1.60 kilometer 
1 Fathom  1.8 meter 
1 Chain  20.11 meter 
1 Nautical mile  1.85 kilometer 
1 Angstrom  10^{10} 
1 Square feet  0.09 square meter 
1 Square inch  6.45 sq. centimeter 
1 Square yard  0.83 square meter 
1 Acre  10^{4} sq. meter 
1 Square mile  2.58 sq. kilometer 
1 Cubic inch  16.38 cubic centimeter 
1 Cubic foot  .028 cubic meter 
1 Cubic yard  0.7 cubic meter 
1 Litre  1000 cubic centimeter 
1 Pint  0.56 liter 
1 Grain  64.8 milligram 
1 Dram  1.77 gm 
1 Ounce  28.35 gm 
1 Pound  0.4537 kilogram 
1 dyne  10^{5} 
1 Poundal  0.1383 newton 
1 erg  10^{7 joule} 
1 Horsepower  747 Watt 
1 Fathom  6 feet 
1 Mile  8 furlong 
1 Mile  5280 feet 
1 nautical mile  6080 feet 
1 foot  12 inch 
1 yard  3 feet 
37°centigrade  98.6° Fahrenheit 
40° Fahrenheit  40° Centigrade 
0° Centigrade  32° Fahrenheit 
FREQUENTLY ASKED QUESTIONS (FAQ)
What is necessary for a physical quantity to be a fundamental unit?
answer: it should be
 well defined
 easy to reproduce
 easy to compare
 internationally accepted
 independent of changes in physical condition
What is a unit in physics?
answer: The chosen standard used for measuring a physical quantity is called unit.
How many types of units are there in physics?
answer: there are two types of units in physics
 Fundamental unit
 Derived unit
What is the system of units?
answer: Internationally accepted chosen standard used for measuring a physical quantity is called the system of units.
How many systems of units are there?
answer: There are four systems of units.
 CGS SYSTEM
 MKS SYSTEM
 FPS SYSTEM
 SI UNITS
What is the full form of the CGS unit in physics?
answer: CENTIMETERGRAMSECOND.
What is the full form of the MKS unit in physics?
answer: METERKILOGRAMSECOND.
What is the full form of the FPS unit in physics?
answer: FOOTPOUNDSECOND.
What is the full form of the SI units in physics?
answer: STANDARD INTERNATIONAL UNITS.
How many fundamental units are there?
answer: There are seven fundamental units in SI units. which are:
 Length
 Mass
 Time
 Electric Current
 Temperature
 Luminous Intensity
 Amount of Substance.
What is the SI unit of Length?
answer: meter/metre.
What is the SI unit of Mass?
answer: Kilogram.
What is the SI unit of Time?
answer: Second.
What is the SI unit of Electric Current?
answer: Ampere.
What is the SI unit of Temperature?
answer: Kelvin.
What is the SI unit of Luminous Intensity?
answer: Candela.
What is the SI unit of Amount of Substance?
answer: Mole.
How many Supplementary units are there?
answer: There are two supplementary units. Radian and Steradian.
What is Radian in physics?
answer: Radian is a supplementary unit used for measuring Plane Angle.
What is Steradian in physics?
answer: Steradian is a supplementary unit used for measuring Solid Angle.
What is a Derived unit?
answer: A unit that is expressed in terms of the fundamental unit is called a derived unit. simply, it is carried from a mathematical combination of SI base units.
What are the two important examples of Derived units?
answer: Force and Work.
What is the relation between SI and CGS unit of Force?
answer: SI unit of Force is Newton and its CGS unit is Dyne. The relation between SI and CGS unit of Force is that 1 newton = 105 dyne.
What is the relation between SI and CGS unit of work?
answer: SI unit of work is erg and its CGS unit is the joule. The relation between SI and CGS unit of Work is that 1 joule = 107 erg.
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