# Resistivity question help

Discussion in 'Electronics Homework Help' started by Tea cup, Mar 22, 2018.

1. ### Tea cup

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Mar 22, 2018
The question is : Copper wire, with a diameter of 1.5mm, must be of such a length as to give a resistance of 0.6 ohms. calculate the length of this wire. Take the resistivity of copper as 0.017 microhm metres.

2. ### Harald KappModeratorModerator

10,079
2,153
Nov 17, 2011
resistance = resistivity / cross sectional area * length
reverse this equation to get the length from a given resistance.

3. ### WHONOES

910
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May 20, 2017
If I remember correctly, the 0.017μΩ meters refers to a 1 Metre cube of solid copper. Calculate from there.

4. ### Harald KappModeratorModerator

10,079
2,153
Nov 17, 2011
That would be valid for a cube of any size...

5. ### WHONOES

910
226
May 20, 2017
No, I think it refers to the actual resistance of the said 1 Metre cube.

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Mar 22, 2018

7. ### Ratch

1,075
327
Mar 10, 2013
Resistivity is an intrinsic property of a material and does not depend on the resistance value of any size or shape. In other words, a cubic foot has the same resistivity as a cubic meter of the same material.

Ratch

8. ### Ratch

1,075
327
Mar 10, 2013
Calculations are straight forward. Keep the units consistent.

Ratch

9. ### The Electrician

112
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Jul 6, 2012
If by the phrase "resistance of the said 1 Metre cube", you mean the resistance measured between two of the plane surfaces of the cube which are on opposite sides of the cube with a perfect conductor used to make the connection to each face, you should be aware that the resistance will be the same for any size cube.