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.
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.
Measurement of any physical quantity involves comparison with a certain basic arbitrarily chosen and widely accepted reference standard called unit.
It is based on the following seven basic/fundamental units and two supplementary units.
Basic/ Fundamental Units
|Physical Quantity||SI Unit||Symbol|
|Amount of substance||mole||mol|
|Physical Quantity||Name of Units||Symbol|
|Physical Quantity||cgs units||SI Unit||Relation|
|Force||dyne||newton||1 newton = 105 dyne|
|Work||erg||joule||1 joule = 107 erg|
What is light year?
It is a distance travelled by light in one year in vacuum.
|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
|1 Micron||1 µm = 10-6 m|
|1 Angstron (Å)||10-10 m|
|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 Chandrashekhar limit||1.4 times the mass of sun = 2.8 × 1030 kg|
|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
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