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 = 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 |
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