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'''Electrical resistance''' is a measure of how much a substance impedes the flow of [[electrons]].<ref>http://www.answers.com/topic/electrical-resistance-1</ref> Resistance is represented with the symbol ''R'', and its [[SI]] unit is the [[Ohm]] (Ω).
'''Electrical resistance''' is a measure of how much a substance impedes the flow of [[electrons]].<ref>http://www.answers.com/topic/electrical-resistance-1</ref> Resistance is represented with the symbol ''R'', and its [[SI]] unit is the [[Ohm]] (Ω).
Resistance in a circuit can be calculated by the [[voltage]] divided by the [[current]] (R = V / I).
Resistance is caused when the free current carrying electrons in a material are scattered due to collisions the ion lattice. These collisions are caused by defects and imperfections in the lattice, and by the lattice vibrations. The resistance of an object is therefore given by
<math>R=\frac{L\rho}{A}</math>
where L is the length of the object, and A is its cross sectional area. \rho is the resistivity of the material the object, and is a measure of how much the free electrons in a material are scattered by the ion lattice.
Resistance in a circuit made of purely resistive elements (i.e no [[inductors]] or [[capacitors]]) can be calculated by the [[voltage]] divided by the [[current]] (R = V / I).
==See Also==
==See Also==