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# Conductor Resistivity

When a small amount of Cu is added to a Ni conductor, then the?

a) Resistivity of Ni will decrease at all temperatures because Cu is better conductor than Ni

b) Residual resistivity of Ni at low temperatures will increase as Cu atoms acts as defect centers

c) Resistivity of Ni will increase at all temperatures as Cu destroys the periodicity of Ni and acts as defects

d) Resistivity of Ni remains unaltered as Cu atoms give the same numbers of free electrons as Ni atoms
Asked by: parag12345 | Member Since Apr-2009 | Asked on: Apr 12th, 2009

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Lokesh M

Answered On : Jan 3rd, 2013

If a small amount of Cu is added to Ni conductor, then resistivity of Ni will increase at all temperatures as Cu destroys the periodicity of Ni and acts as defects.

According to Matthiessen rule, electrical resistivity is the sum of two
components: a residual part Pr, and a thermal part Pt

Impurities increases the residual resistivity. Nordheims rule for residual resistivity
helps us the determine the increase in resistivity due to impurities.

Equation for Nordheims rule
is given by:

Pr(x) = A x(1-x)

Where Pr is the residual resistivity,
x is the percentage of impurity

A is the constant that is dependent on impurity and conductor.It depends on the base metal and the impurity. The material factors that influence the constant A includes atomic sizes, crystal structures and electro-negativities.

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