ADVANTAGES OF SI Units

• ADVANTAGES OF SI Units
• SI is one of the largest system of unit. It has many advantages over other system of units like MKS or FPS or CGS. Few of them are enlisted below

1. SI is a coherent system of units i.e. a system based on a certain set of fundamental

units, from which all derived units are obtained by multiplication or division without

introducing numerical factors i.e. units of a given quantity are related to one another

by powers of 10.

2. SI is a rational system of units, as it assigns only one unit to a particular physical

quantity.

For example joule is the unit for all types of energy. This is not so in other systems of

units. e.g. in MKS system, mechanical energy is in joule, heat energy is in calorie and

electric energy is in watt hour.

3. SI is an absolute system of units. There are no gravitational units on the system.

The use of factor ‘g’ is thus eliminated.

4. S.1 is a metric system i.e. the multiples and sub multiples of units are expressed as

powers of 10.

5. In current electricity, the absolute units on the S.I, like ampere for current, volt for

potential difference, ohm for resistance, Henry for inductance, farad for capacity arid

so on, happen to be the practical units for measurement of these quantities.

6. SI is an internationally accepted system

SOME MORE COSMOLOGICAL  UNITS OF DISTANCE:
1. Astronomical Unit (A.U.) : The average distance between the centre of the sun
to the centre of the earth is known as one A.U.
1 A.U. = 1.496* 10 RACE TO POWER 11
 1.5 1011 m
2. Light Year (l.y.) : One light year is the distance travelled by light in vacuum in
one year.
1 l.y. = 3* 10 RACE TO POWER 8 * (365* 24  *60 * 60)
= 9.46 * 10 RACE TO POWER 15 m
3. Par sec (Parallactic Second): One Par sec is the distance at which an arc of 1A.U.
long subtends an angle of 1 second.
1 Parsec = 3.084* 10 RACE TO POWER 16 m