**STANDARD UNITS OF MEASUREMENT IN PHYSICS PDF**

**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.

**Unit**

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

- well defined
- easy to reproduce
- easy to compare
- internationally accepted
- 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 = 10^{5} dyne |

Work | erg | joule | 1 joule = 10^{7} 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 × 10^{15} m |

1 parsec |
3.084 × 10^{16} m = 3.26 ly |

1 Astronomical Unit (A.U) |
1.5 × 10^{11} 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 |
10^{3} kg |

1 Quintal |
10^{2} 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 × 10^{30} 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 | 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} |

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

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