Introduction to SI Units and Conversion Factors , Advantages and Disadvantages

Introduction to SI Units and Conversion Factors

SALIENT FEATURES OF SI UNITS

1. It is a coherent system of units, i.e., product or quotient of any two base quantities

results in a unit resultant quantity. For example, unit length divided by unit time

gives unit velocity.

2. It is a rationalised system of units, applicable to both, magnetism and electricity.

3. It is a non-gravitational system of units. It clearly distinguishes between the units

of mass and weight (force) which are kilogram and newton respectively.

4. AII the units of the system can be derived from the base and supplementary

units.

5. The decimal relationship between units of same quantity makes possible to express

any small or large quantity as a power of 10.

Advantages of Sl Units

1. Units for many different quantities are related through a series of simple and basic relationship.

2. Being an absolute system, it avoids the use of factor 'g' i.e. acceleration due to gravity in several expressions in physics and engineering which had been a nuisance in all numericals in physics and engineering.

3. Being a rationalised system, it ensures all the advantages of rationalised MKSA system in the fields of electricity, magnetism, electrical engineering and electronics.

4. ]oule is the only sole unit of energy of all forms and watt is the sole unit of Power

hence a lot of labour is saved in calculations.

5. It is a coherent system of units and involves only decimal co-efficients. Hence it is very convenient and quick system for calculations.

Disadvantages Of SI Units

L. The non-Sl time units'minute'and'hour'will still continue to be used until the clocks and watches are all changed to kilo seconds and mega seconds etc.

2. The base unit kilogram (kg) includes a prefix, which creates an ambiguity in the

use of multiPliers with gram.

3. SI units for energy, power and pressure (i.e., ioule, watt and pascal) are too small to be expressed in icience and technolory, and, therefore, in such cases the use of largei units, such as Mj, kW, kPa, will have to be made'

4. There are difficulties with regard to developing new SI units for apparent and

reactive energy while joule is the accepted unit for active energy in SI systems.