ABSTRACT

A question concerning the Standard International (SI) units is a popular opening to the physics structured oral examination and candidates should understand the relationship between derived and base units and be comfortable in manipulating them from one to other. By the 1960s, the International System of Units was developed which incorporated six base units along with rules for the use of derived units and prefixes. The advantage of this unified system is that equations and calculations will produce answers in the appropriate SI unit. There are seven base units, which are considered to be dimensionally independent: length, mass time, current, temperature, amount of substance and luminous intensity. The plane angle and solid angle were supplementary units but the category was abolished in 1995. These units are considered named derived units. Derived units are formed by combination of various base units according to mathematical relationships which link these quantities. Derived units are: area, volume, density and acceleration.