In 1960, the Conférence Générale des Poids et Mesures (11th CGPM), which is the international authority on the metric system, replaced all previous systems with the modern metric system officially named the Système International d’Unités, abbreviated to SI. Over the years, this metric system has been adopted throughout the world and is continually being revised to parallel developments in science and technology.
The SI is founded on seven base units ( Table App. 1 ). Other derived units are defined in terms of the seven base units and, for ease of understanding and convenience, may have special or compound names and their own symbols ( Tables App. 2 and App. 3 ). There are also 20 SI prefixes used to form decimal multiples and submultiples ( Table App. 4 ).
Table App. 1
The Seven Base Units of the SI
Physical Quantity
Base Unit
Symbol
Amount of substance
mole
mol
Electric current
ampere
A
Length
meter
m
Luminous intensity
candela
cd
Mass
kilogram
kg
Thermodynamic temperature
kelvin
K
Time
second
s
Table App. 2
Examples of SI-Derived Units with Special Names
Physical Quantity
Unit Name
Symbol
Expressed in Base Units
Plane angle
radian
rad
m m –1 = 1
Solid angle
steradian
sr
m 2 m –2 = 1
Frequency
hertz
Hz
s –1
Force
Newton
N
m kg s –2
Work/energy
joule
J
m 2 kg s –2 (N m)
Pressure/stress
pascal
Pa
m –1 kg s –2 (N m –2 )
Power
watt
W
m 2 kg s –3 (J s –1 )
Electric charge
coulomb
C
s A
Electric potential difference
volt
V
m 2 kg s –3 A –1 (W A –1 )
Electric capacitance
farad
F
m –2 kg –1 s 4 A 2 (C V –1 )
Electric resistance
ohm
Ω
m 2 kg s –3 A –2 [V/A]
Electric conductance
siemens
S
m –2 kg –1 s 3 A 2 [A/V]
Magnetic flux
weber
Wb
m 2 kg s –2 A –1
Magnetic induction
tesla
T
kg s –2 A –1 (Wb m –2 )
Inductance
henry
H
m 2 kg s –2 A –2 (Wb A –1 )
Luminous flux
lumen
Im
cd sr
Illuminance
lux
Ix
cd sr m –2
Table App. 3
SI Units with Compound Names
Physical Quantity
Name of Unit
Symbol
Area
square meter
m 2
Volume
cubic meter
m 3
Speed/velocity
meter per second
m s –1
Acceleration
meter per second squared
m s –2
Density
kilogram per cubic meter
kg m –3
Electric field strength
volt per meter
V m –1
Magnetic field strength
ampere per meter
A m –1
Current density
ampere per meter squared
A m –2
Specific heat capacity
joule per kilogram per kelvin
J kg –1 K –1
Table App. 4
The 20 SI Prefixes
Prefix
Symbol
Ordinary Notation
10 x
yotta-
Y
1,000,000,000,000,000,000,000,000
10 24
zetta-
Z
1,000,000,000,000,000,000,000
10 21
exa-
E
1,000,000,000,000,000,000
10 18
peta-
P
1,000,000,000,000,000
10 15
tera-
T
1,000,000,000,000
10 12
giga-
G
1,000,000,000
10 9
mega-
M
1,000,000
10 6
kilo-
k
1,000
103
hecto-
h
100
10 2
deca-
da
10
10 1
1
10 0
deci-
d
0.1
10 –1
centi-
c
0.01
10 –2
milli-
m
0.001
10 –3
micro-
μ
0.000 001
10 –6
nano-
n
0.000 000 001
10 –9
pico-
P
0.000 000 000 001
10 –12
femto-
f
0.000 000 000 000 001
10 –15
atto-
a
0.000 000 000 000 000 001
10 –18
zepto-
z
0.000 000 000 000 000 000 001
10 –21
yocto-
y
0.000 000 000 000 000 000 000 001
10 –24
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