SI unit is same everywhere as in cgs unit there are different unit of measurement . SI unit is adopted internationally and the units are fixed and do not change at any place.

(i) SI is coherent system of units, i.e., a system based on certain set of fundamental units. (ii) SI is rational system of units. i.e., it assigns only one unit to a particular physical quantity. (iii) SI is metric system, i.e., multiples and sub-multiples of the system can be expressed as a power of 10.

What are the characteristics of SI units?

• It should be well defined.
• It should be of suitable size such as neither too large nor too small in comparison to the quantity to be measured.
• It should be easily reproducible at all places.
• It should not change with time and from place to place.

(i) It is a rational system, in which only one unit is used for one physical quantity. (ii) It is a coherent system, which means all the derived units can be easily obtained form basic and supplementary units. (iii) It is a metric system which means that multiples and submiltiples can be expressed as powers of 10.

Base units are defined by a particular process of measuring a base quantity whereas derived units are defined as algebraic combinations of base units. b. A base quantity is chosen by convention and practical considerations. Derived quantities are expressed as algebraic combinations of base quantities.

SI-Derived Units

There are seven basic units in the SI system: the meter (m), the kilogram (kg), the second (s), the kelvin (K), the ampere (A), the mole (mol), and the candela (cd).