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

AI Thread Summary
The discussion centers on calculating the thickness of a copper layer deposited on a constantan wire, which reduces the wire's resistance to one-third of its original value. The resistivities of constantan and copper are provided, along with the wire's radius. Participants emphasize that the two materials act in parallel, suggesting that the cross-sectional area of the copper should be calculated as the difference between the areas of the larger and smaller wires. The conversation includes hints and confirmations about the approach to solving the problem. Ultimately, the focus is on applying the resistance formula and understanding the geometry of the wire layers.
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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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