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International System of Units
Definitions of SI Base Units
- Meter
- The meter is the length of path travelled by light in vacuum
during a time interval of 1/299 792 458 of a second (17th CGMP,
1983).
- Kilogram
- The kilogram is the unit of mass: it is equal to the mass of
the international prototype of the kilogram (3rd CGMP, 1901)
- Second
- The second is the duration of 9 192 631 770 periods of the
radiation corresponding to the transition between the two hyperfine
levels of the ground state of the cesium-133 atom (13th CGMP,
1967).
- Ampere
- The ampere is that constant current which, if maintained in two
straight parallel coductors of infinite length, of negligible
circular cross-section, and placed 1 meter apart in vacuum, would
produce between these conductors a force equal to 2 x
10-7 newton per meter of length (9th CGPM, 1948)
- Kelvin
- The kelvin, unit of thermodynamic temperature, is the fraction
1/273,16 of the thermodynamic temperature of the triple point of
water (13th CGMP)
- Mole
- The mole is the amount of substances of a system which contains
as many elementary entities as there are atoms in 0,012 kilogram of
carbon-12. When the mole is used, the elementary entities must be
specified and may be atoms, molecules, ions, electrons, other
particles, or specific groups of such particles (14th
CGPM,1971).
- Candela
- The candela is the luminous intensity, in a given direction, of
a source that emits monochromatic radiation of frequency 540 x
1012 hertz and that has a radiant intensity in that
direction of (1/683) watt per steradian (16th CGPM, 1979).
Names and Symbols for the SI Base Units
| Physical quantity |
Name of SI unit |
Symbol for SI unit |
| length |
meter |
m |
| mass |
kilogram |
kg |
| time |
second |
s |
| electric current |
ampere |
A |
| thermodynamic temperature |
kelvin |
K |
| amount of substance |
mole |
mol |
| luminous intensity |
candela |
cd |
SI Derived Units with Special Names and Symbols
|
|
Name of |
Symbol for |
Expression in |
| Physical Quantity |
SI unit |
SI Unit |
terms of SI base units |
| frequency |
hertz |
Hz |
s-1 |
| force |
newton |
N |
m kg s-2 |
| pressure, stress |
pascal |
Pa |
N m-2 |
= m-1 kg s-2 |
| energy, work, heat |
joule |
J |
N m |
= m2 kg s-2 |
| power, radiant flux |
watt |
W |
J s-1 |
= m2 kg s-3 |
| electric charge |
coulomb |
C |
A s |
| electric potential, |
volt |
V |
J C-1 |
= m2 kg s-3 A-1 |
| (electromotive force) |
| electric resistance |
ohm |
W |
V A-1 |
= m2 kg s-3 A-2 |
| electric conductance |
siemens |
S |
W-1 |
= m-2 kg-1 s3
A-2 |
| electric capacity |
farad |
F |
C V-1 |
= m-2 kg-1 s4
A2 |
| magnetic flux density |
tesla |
T |
V s m-2 |
= kg s-2 A-1 |
| magnetic flux |
weber |
Wb |
V s |
= m2 kg s-2 A-1 |
| inductance |
henry |
H |
V A-1 s |
= m2 kg s-2 A-2 |
| Celsius temperature |
degree Celsius |
°C |
K |
| luminous flux |
lumen |
lm |
cd sr |
| illuminance |
lux |
lx |
cd sr m-2 |
| activity (radioactice) |
becquerel |
Bq |
s-1 |
| absorbed dose (of radiation) |
gray |
Gy |
J kg-1 |
= m2 s-2 |
| dose equivalent |
sievert |
Sv |
J kg-1 |
= m2 s-2 |
| (dose of equivalent index) |
| plane angle |
radian |
rad |
1 |
= m m-1 |
| solid angle |
steradian |
sr |
1 |
= m2 m-2 |
SI Prefixes
| Factor |
Prefix |
Symbol |
|
Factor |
Prefix |
Symbol |
| 1024 |
yotta |
Y |
|
10-1 |
deci |
d |
| 1021 |
zetta |
Z |
|
10-2 |
centi |
c |
| 1018 |
exa |
E |
|
10-3 |
milli |
m |
| 1015 |
peta |
P |
|
10-6 |
micro |
m |
| 1012 |
tera |
T |
|
10-9 |
nano |
n |
| 109 |
giga |
G |
|
10-12 |
pico |
p |
| 106 |
mega |
M |
|
10-15 |
femto |
f |
| 103 |
kilo |
k |
|
10-18 |
atto |
a |
| 102 |
hecto |
h |
|
10-21 |
zepto |
z |
| 101 |
deca |
da |
|
10-24 |
yocto |
y |
© 10.02.2003 by Florian Häußermann. No rights
reserved.
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