ABSTRACT
The basic units in the SI system are listed below with their symbols:
Quantity Unit
length metre, m mass kilogram, kg time second, s electric current ampere, A thermodynamic temperature kelvin, K luminous intensity candela, cd amount of substance mole, mol
Derived SI units use combinations of basic units and there are many of them. Two examples are:
Acceleration – metres per second squared (m/s2)
SI units may be made larger or smaller by using prefixes which denote multiplication or division by a particular amount. The six most common multiples, with their meaning, are listed below:
Prefix Name Meaning
M mega multiply by 1 000 000 (i.e. ð 106) k kilo multiply by 1000 (i.e. ð 103) m milli divide by 1000 (i.e. ð 103) μ micro divide by 1 000 000 (i.e. ð 106) n nano divide by 1 000 000 000
(i.e. ð 109) p pico divide by 1 000 000 000 000
(i.e. ð 1012)
1.2 Charge The unit of charge is the coulomb (C) where coulomb D
6.24 ð 1018 electrons). The coulomb is defined as the quantity of electricity which flows past a given point in an electric circuit when a current of one ampere is maintained for one second. Thus,
charge, in coulombs Q = It
where I is the current in amperes and t is the time in seconds.
