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Revision as of 09:20, 8 March 2004 editHadal (talk | contribs)Administrators31,685 editsm Reverted edits by 81.132.143.234 to last version by Perl← Previous edit Revision as of 09:26, 10 March 2004 edit undoHeron (talk | contribs)Administrators29,253 edits distinguished between resistance and differential resistanceNext edit →
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'''Electrical resistance''' is the ratio of the ] (i.e. voltage) across an electric component (such as a ]) to the ] passing through it: '''Electrical resistance''' is the ratio of the ] (i.e. voltage) across an electric component (such as a ]) to the ] passing through it:


:<math>\mathbf R=V/I</math> :<math>R=V/I</math>


⚫ where ''R'' is the resistance, ''V'' the voltage and ''I'' the current.
or


⚫ Resistance is thus a measure of the component's opposition to the flow of ]. The ] unit of electrical resistance is the ]. Its ] quantity is '''electrical conductance''' measured in ].
⚫ :<math>\mathbf R=\delta V/I</math>


'''Differential resistance''' or '''incremental resistance''' is defined as the slope of the ''V-I'' graph at a particular point, thus:
⚫ (where V is the voltage and I the current)


⚫ :<math>R=dV/dI</math>
⚫ It is thus a measure of the component's opposition to the flow of ]. Electrical resistance is usually denoted by the symbol ''R''. The ] unit for electrical resistance is ]. Its ] quantity is '''electrical conductance''' measured in ].


This quantity is sometimes called simply ''resistance'', although the two definitions are equivalent only for an ohmic component such as an ideal resistor. If the ''V-I'' graph is not monotonic (i.e. it has a peak or a trough), the differential resistance will be negative for some values of voltage and current. This property is often known as '']'', although it is more correctly called ''negative differential resistance'', since the absolute resistance ''V''/''I'' is still positive.
⚫ For a wide variety of materials and conditions, the electrical resistance does not depend on the amount of current flowing or the amount of applied ]: the two are ] and the proportionality constant is the electrical resistance. This is the content of ].


⚫ For a wide variety of materials and conditions, the electrical resistance does not depend on the amount of current flowing or the amount of applied ]: the two are ] and the proportionality constant is the electrical resistance. This case is described by ].
⚫ Specific electrical resistance, a measure of a material's ability to oppose the flow of electric current, is also known as ].

⚫ '''Specific electrical resistance''', a measure of a material's ability to oppose the flow of electric current, is also known as ].


The resistance ''R'' of a wire can be computed as The resistance ''R'' of a wire can be computed as
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See ] for the more information about the physical mechanisms for conduction in materials. See ] for the more information about the physical mechanisms for conduction in materials.

Some materials exhibit the property known as ].


==See also== ==See also==
*]
*] *]

Revision as of 09:26, 10 March 2004


Electrical resistance is the ratio of the potential difference (i.e. voltage) across an electric component (such as a resistor) to the current passing through it:

R = V / I {\displaystyle R=V/I}

where R is the resistance, V the voltage and I the current.

Resistance is thus a measure of the component's opposition to the flow of electric charge. The SI unit of electrical resistance is the ohm. Its reciprocal quantity is electrical conductance measured in siemens.

Differential resistance or incremental resistance is defined as the slope of the V-I graph at a particular point, thus:

R = d V / d I {\displaystyle R=dV/dI}

This quantity is sometimes called simply resistance, although the two definitions are equivalent only for an ohmic component such as an ideal resistor. If the V-I graph is not monotonic (i.e. it has a peak or a trough), the differential resistance will be negative for some values of voltage and current. This property is often known as negative resistance, although it is more correctly called negative differential resistance, since the absolute resistance V/I is still positive.

For a wide variety of materials and conditions, the electrical resistance does not depend on the amount of current flowing or the amount of applied voltage: the two are proportional and the proportionality constant is the electrical resistance. This case is described by Ohm's law.

Specific electrical resistance, a measure of a material's ability to oppose the flow of electric current, is also known as electrical resistivity.

The resistance R of a wire can be computed as

R = L ρ A , {\displaystyle R={L\rho \over A}\;,}

where L is the length of the wire, A is the cross-sectional area and ρ is the electrical resistivity of the material.

See electrical conduction for the more information about the physical mechanisms for conduction in materials.

See also