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metre [m]
The metre is
the basic
unit of
length. It
is the
distance
light
travels, in
a vacuum, in
1/299792458th
of a second.
kilogram
[kg]
The kilogram
is the basic
unit of
mass. It is
the mass of
an
international
prototype in
the form of
a
platinum-iridium
cylinder
kept at
Sevres in
France.
It is now
the only
basic unit
still
defined in
terms of a
material
object, and
also the
only one
with a
prefix[kilo]
already in
place.
second [s]
The second
is the basic
unit of
time. It is
the length
of time
taken for
9192631770
periods of
vibration of
the
caesium-133
atom to
occur.
ampere [A]
The ampere
is the basic
unit of
electric
current. It
is that
current
which
produces a
specified
force
between two
parallel
wires which
are 1 metre
apart in a
vacuum.It
is named
after the
French
physicist
Andre Ampere
(1775-1836).
kelvin [K]
The kelvin
is the basic
unit of
temperature.
It is 1/273.16th
of the
thermodynamic
temperature
of the
triple point
of water.
It is named
after the
Scottish
mathematician
and
physicist
William
Thomson 1st
Lord Kelvin
(1824-1907).
mole [mol]
The mole is
the basic
unit of
substance.
It is the
amount of
substance
that
contains as
many
elementary
units as
there are
atoms in 0.012
kg of
carbon-12.
candela [cd]
The candela
is the basic
unit of
luminous
intensity.
It is the
intensity of
a source of
light of a
specified
frequency,
which gives
a specified
amount of
power in a
given
direction.
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