What is the thickness of the copper layer on a constantan wire?

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Homework Help Overview

The problem involves determining the thickness of a copper layer deposited on a constantan wire, which affects the wire's resistance. The context includes the resistivities of both materials and the relationship between resistance and cross-sectional area.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the relationship between the resistances of the two materials and how they are configured, particularly considering the parallel arrangement of the layers. There is a question regarding the treatment of the cross-sectional area of the copper layer.

Discussion Status

Some participants have offered hints about the configuration of the layers and have confirmed the approach regarding the cross-sectional area. The discussion is ongoing with various interpretations being explored.

Contextual Notes

Participants are considering the implications of the resistivity values provided and how the geometry of the wire changes with the addition of the copper layer. There may be constraints related to the assumptions made about the wire's dimensions and the uniformity of the copper layer.

mysqlpress
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Homework Statement



Here's the problem.
The resistance of a piece of constantan wire of radius 0.6mm is reduced to 1/3 its original resistance when a unifrom layer of copper is deposited on it. Find the thickness of the layer of copper
(Resistivity of constantan = 49*10^-8 ohm m
resistivity of copper =1.7*10^-8 ohm m

Homework Equations



I do think that it is related to
R =pl/A where p is the resistivity , l = length of wire
A = cross-section area

The Attempt at a Solution


I've tried ... but don't know how to work out
...
Thanks
 
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Hint: The two layers are in parallel.
 
Doc Al said:
Hint: The two layers are in parallel.

Yup.. and
Should I treated the cross-section area of copper as ( cross-section area of a big wire - cs a of a small wire) ? Since it is deposited .. I think on the surface of the constantan..covered it out...
 
mysqlpress said:
Should I treated the cross-section area of copper as ( cross-section area of a big wire - cs a of a small wire) ?
Sure.
 
Doc Al said:
Sure.

Okay, Thanks for your guide~~ :)
 

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