A resistor
is a two-terminal electrical component used in electronic circuits to
oppose the flow of an electric current. Resistors are normally
characterized by
their resistance, maximum power they can dissipate, maximum working
voltage, temperature
coefficient, noise, and parasitic inductance. If an object inserted in
a circuit displays a current flow which is proportional to the
voltage across it, the ratio of voltage V
divided by current I
will be constant. This constant ratio is called resistance R=V/I.
In
an ideal resistor R
does not depend on the
current.
The Ohm's law states that I=V/R.
Since this is true only for so called electrical conductors, in reality
the Ohm's
law means that there are substances,
including solids and liquids, that display this kind
of behavior, at least within certain range of currents.
The SI unit of
electrical resistance is the ohm,
symbol Ω. Its reciprocal quantity is conductance measured in
siemens. Electronic industry often uses a special coding system of
colored stripes to indicate the component's value and tolerance (see resistor
color chart). These
markings were originally published by Electronic Industries
Alliance as EIA-RS-279, and currently are specified by IEC 60062 Ed.
5.0.
This graphical calculator works
both ways- you can get resistances from color codes or generate
the color bands from resistor values (5%, 10% and 20% tolerance). |
