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International System of Measurement, Units and Efficiency
Contents
1
...
2 Derived Units
1
...
4 Summary

1
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It is the primary system of measurement used by most countries around the
world
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The International System is made up of 7 base units:
Quantity
Mass
Length
Time
Electric Current
Absolute Temperature
Luminous Intensity
Amount of Substance

Symbol
M
Ɩ
t
I
K
I
n

Unit
Kilograms (kg)
Metres (m)
Seconds (s)
Amperes (A)
Kelvin (K)
Candela (Cd)
Moles (mol)

These units are based on physical quantities1:
Mass: the kilogram is the mass of a platinum-iridium cylinder kept at the International Bureau of
Weights and Measures near Paris
...
73 wavelengths of the orange line in the spectrum of an
internationally specified krypton discharge lamp
Time: the second is the interval of time in which the radiation corresponding to the transition of the
caesium-133 atom cycles 9,192,631,770 times
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1

Hughes Electrical and Electronic Technology, International System of Measurement (p
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16 of the thermodynamic temperature of the triple point
of water
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01°C, therefore
0°C = 273
...

Amount of Substance: A mole is the amount of substance containing as many elementary entities as
there are atoms in exactly 0
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1
...
1 can be manipulated to give derived units for other quantities
...
For example, velocity is
calculated by dividing distance by time
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Simple derived units include:
Quantity
Area
Volume
Velocity
Acceleration

Symbol
A
V
u
a

Unit
m2
m3
m/s
m/s2

These are clearly just products or quotients (or both) of base units
...
This coherence is what makes the SI so useful in comparison to the imperial system, as no
conversions between units are required
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3 Efficiency
When a system transforms energy, some of that energy is consumed in order to make the system
operate
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Efficiency is often given as a percentage, which can be found by multiplying the value of efficiency by
100
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4 Summary

The coherent International System of Measurement is made up of 7 base units, and of derived units
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𝜂=

𝑃𝑜𝑤𝑒𝑟 𝑜𝑢𝑡𝑝𝑢𝑡
𝑃𝑂
=
𝑃𝑜𝑤𝑒𝑟 𝑖𝑛𝑝𝑢𝑡
𝑃𝐼

References and Further Reading:
E
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3-11)



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