The Physics Factbook™
Edited by Glenn Elert -- Written by his students
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|Faughn, Jerry S., Raymond A. Serway. College Physics. Pacific Grove, CA: Thomson Learning Inc, 2003: 538.||
|1.50 × 10-6 Ωm|
|Nichrome. Wikipedia, 2007.||
|1.1 × 10-6 Ωm|
|Resistivity: Constantan resistivity and temperature. Schlumberger Limited, 2007.||
|1.00 × 10-6 Ωm|
|Roberston, Ian. Electronics for Electricians and Engineers. New York, NY: Industrial Press, 1987: 34||
|1.10 × 10-6 Ωm|
|The State Education Department. 2006 Edition Reference Table for Physical Science Setting/Physics. Albany, New York: DOE. 2006-2007.||
|1.50 × 10-6 Ωm|
Resistivity is a measure of how strongly a material opposes the flow of electric current. Good electrical conductors have very low resistivities and good insulators have very high resistivities. Resistivity is denoted by the Greek symbol rho (ρ) and can be determined by rearranging this formula:
R = ρl / A
where ρ is called the resistivity of the material, R is the resistance, l is the length and A represents a cross-sectional area. The unit of resistivity is then ohm-meters (Ωm).
Nichrome, a non-magnetic alloy that is commonly made up of 80% nickel and 20% chromium, has a resistivity ranging from 1.10 × 10-6 Ωm to 1.50 × 10-6 Ωm (0.00000110 Ωm to 0.00000150 Ωm) and a very high boiling point (~1400 °C). With such a low resistivity and high boiling point, this makes nichrome a very good conductor of electricity and ideal material for making wires and other insulation devices.
Nichrome is commonly wound up into coils and used in heating elements (devices that convert heat into electricity through Joule heating) such as hair dryers, toasters and ovens. However, nichrome wires are not used as much as copper wires (resistivity = 1.7 × 10-8 Ωm) due to the high cost of chromium.
Harvey Kwan -- 2007
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