From the 7 basic units
of the SI other units
are derived for a
variety of purposes.
Only a few of are
explained here as
examples, there are many
more.
**farad [F]**
The farad is
the SI unit
of the
capacitance
of an
electrical
system, that
is, its
capacity to
store
electricity.
It is a
rather large
unit as
defined and
is more
often used
as a
microfarad. It is
named after
the English
chemist and
physicist
Michael
Faraday
(1791-1867).
**hertz [Hz]**
The hertz is
the SI unit
of the
frequency of
a periodic
phenomenon.
One hertz
indicates
that 1 cycle
of the
phenomenon
occurs every **second**.
For most
work much
higher
frequencies
are needed
such as the
kilohertz
[kHz] and
megahertz
[MHz]. It
is named
after the
German
physicist
Heinrich
Rudolph
Hertz
(1857-94).
**joule [J]**
The joule is
the SI unit
of work or
energy. One
joule is the
amount of
work done
when an
applied
force of 1 **newton**
moves
through a
distance of
1 **metre**
in the
direction of
the force.
It is named
after the
English
physicist
James
Prescott
Joule
(1818-89).
**newton [N]**
The newton
is the SI
unit of
force. One
newton is
the force
required to
give a mass
of 1 **kilogram**
an
acceleration
of 1
**metre**
per **second**
per
**second**. It is
named after
the English
mathematician
and
physicist
Sir Isaac
Newton
(1642-1727).
**ohm [Ω ]**
The ohm is
the SI unit
of
resistance
of an
electrical
conductor.
Its symbol,
is the
capital
Greek letter
'omega'.
It is named
after the
German
physicist
Georg Simon
Ohm
(1789-1854).
**pascal [Pa]**
The pascal
is the SI
unit of
pressure.
One pascal
is the
pressure
generated by
a force of
1 **newton**
acting on an
area of 1
square
**metre**.
It is a
rather small
unit as
defined and
is more
often used
as a
kilopascal [kPa]. It is
named after
the French
mathematician,
physicist
and
philosopher
Blaise
Pascal
(1623-62).
**volt [V]**
The volt is
the SI unit
of electric
potential.
One volt is
the
difference
of potential
between two
points of an
electrical
conductor
when a
current of 1 **ampere**
flowing
between
those points
dissipates a
power of 1 **watt**.
It is
named after
the Italian
physicist
Count
Alessandro
Giuseppe Anastasio
Volta
(1745-1827).
**watt [W]**
The watt is
used to
measure
power or the
rate of
doing work.
One watt is
a power of
1 **joule**
per
**second**.
It is
named after
the Scottish
engineer
James Watt
(1736-1819). Note that
prefixes
may be used
in
conjunction
with any of
the above units. |