Conventions for the use of SI Units

(2) Full name of a unit always starts with smaller letter even if the name is after a person, e.g., 1 newton, 1 joule, etc. But symbol for unit named after a person

should be in capital letter, e.g., N after

scientist Newton, J after scientist Joule,

etc.

(3) Symbols for units do not take plural form

for example, force of 20 N and not 20

newtons or not 20 Ns.

(4) Symbols for units do not contain any full

stops at the end of recommended letter,

e.g., 25 kg and not 25 kg..

(5) The units of physical quantities in

numerator and denominator should be

written as one ratio for example the SI

unit of acceleration is m/s2

or m s-2 but

not m/s/s.

(6) Use of combination of units and symbols

for units is avoided when physical

quantity is expressed by combination of

two. e.g., The unit J/kg K is correct while

joule/kg K is not correct.

(7) A prefix symbol is used before the symbol

of the unit.

Thus prefix symbol and units symbol

constitute a new symbol for the unit which

can be raised to a positive or negative

power of 10. 1ms = 1 millisecond = 10-3s 1µs = 1 microsecond = 10-6s 1ns = 1 nanosecond = 10-9s Use of double prefixes is avoided when single prefix is available 10-6s =1µs and not 1mms. 10-9s = 1ns and not 1mµs

(8) Space or hyphen must be introduced while indicating multiplication of two units e.g., m/s should be written as m s-1 or m-s-1 and Not as ms-1 (because ms will be read as millisecond).