FUNDAMENTAL UNITS IN PHYSICS แ—2021 [LIST, symbols, BASE SI UNITS, DEFINITION, and Prefixes]

physical quantities and measurement ,  base SI UNIT, prefixes, derived units, Plane angle, solid angle

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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 (m2kg.s-2) J
Energy E joule (m2kg.s-2) J
Electric Current i ampere A
Temperature T kelvin K
Intensity of flame Iv candela cd
Luminous intensity Iv candela cd
Plane Angle radian rad
Solid Angle ฯ‰ steradian sr
Force F newton N
Area A square meter m2
Volume V Cubic meter m3
Speed v meter per second ms-1
Angular velocity ฯ‰ radian per second rad s-1
Frequency f Hertz Hz
Moment of Intertia I kilogram square meter kgm2
Momentum p kilogram meter per second kg ms-1
Impulse J newton second Ns
Angular Momentum L kilogram square meter per second kg m2s-1
Pressure p pascal Pa
Power P watt W
Surface tension ฯƒ (lower case sigma) newton per meter Nm-1
Viscosity ยต, ฮท newton second per square meter N.s.m-2
Thermal Conductivity ฮบ, ฮป, K watt per meter per degree celcius Wm-1C-1
Specific Heat Capacity c joule per kilogram per Kelvin j kg-1K-1
Electric Charge q coulomb C
Potential Difference ฮ”V volt V
Electric Resistance R ohm ฮฉ
Electric Capacity c farad F
Magnetic Induction B henry H
Magnetic Flux ฮฆ weber Wb
Luminous Flux ฮฆv lumen lm
Photometric power ฮฆv lumen lm
Intensity of illumination lx lux lx
Wavelength ฮป angstrom
Astronomical distance au, AU light year ly
Density ฯ kilogram per meter square kg.m-3
Torque ฯ„ Newton meter
Dynamic viscosity ฮท (eta) pascal second pa.s
Acoustic pressure Lpa pascal (kg m-1s-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:-

  1. Well defined
  1. easy to reproduce
  1. easy to compare
  1. internationally accepted
  1. independent of changes in physical conditions
Types of the system of units
 

there are the following internationally accepted systems for measuring the units:

SYSTEM FULL FORM
CGS CENTIMETRE-GRAM-SECOND
MKS METRE-KILOGRAMME-SECOND
FPS FOOT-POUND-SECOND
Base SI UNITS STANDARD INTERNATIONAL UNITS


physical units are of two types:
  1. fundamental units
  2. 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:

  1. radian [red]
  1. 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 ฯ– 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. 


Noteall 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=105 dyne
work erg joule 1 joule=107 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 light-year = 9.46×1015m 1 Metric ton = 103 kg 1 Solar day = 86400 sec.
1 Astronomical unit (A.U.)=1.5×1011m 1 Quintol = 102 kg 1 year = 365½ solar days
1 Parsec = 3.26 light-year i.e. 3.08×1016m 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 = 1ยตm i.e. 10-6m 1 Chandrashekar limit = 1.4 times the mass of sun i.e. 2.8×1030 kg
1 Angstron (ร…) =10-10m



prefixes used in the metric system:

PREFIX SYMBOL VALUE
deci d 10-1
centi  c 10-2
Milli m 10-3
micro ยต 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




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 104 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

  1. Fundamental unit
  2. 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.

  1. CGS SYSTEM
  2. MKS SYSTEM
  3. FPS SYSTEM
  4. SI UNITS

What is the full form of the CGS unit in physics?

answer: CENTIMETER-GRAM-SECOND.

What is the full form of the MKS unit in physics?

answer: METER-KILOGRAM-SECOND.

What is the full form of the FPS unit in physics?

answer: FOOT-POUND-SECOND.

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:-

  1. Length
  2. Mass
  3. Time
  4. Electric Current
  5. Temperature
  6. Luminous Intensity
  7. 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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