- #1

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Resistivity of Copper: .0039

Resistivity of Iron: .0005

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- Thread starter confused1
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- #1

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Resistivity of Copper: .0039

Resistivity of Iron: .0005

- #2

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Try this formula

[tex]\frac{{\Delta R}}{R_0} = \alpha \Delta T[/tex]

You need to look up the alpha

[tex]\frac{{\Delta R}}{R_0} = \alpha \Delta T[/tex]

You need to look up the alpha

- #3

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For pure metals the relationship is (almost) linear and the formula is:

R=R_{0}[1+[tex]\alpha[/tex](T-T_{0})

FYI the figures quote are temperature coefficients measured in K^{-1} (degrees Celsius to the minus one is also fine, as the increments are the same. Just don't mix the two as values for T and T_{0} in one calculation):

Where you want the resistance to be equal, you just back the copper and iron halves of the equation together (copper on the left, iron on the right).

0.501 [1 + 0.0039 (T - 20)] = 0.487 [1 + 0.0005 (T - 20)]

Multiply the lot out, so as to separate T

0.501 + 0.0019539T - 0.039078 = 0.487 + 0.0002435T - 0.00487

Real numbers on the left, expressions in T on the right

0.501 - 0.487 - 0.039078 + 0.00487 = (0.0002435 - 0.0019539)T

-0.020208 = -0.0017104T

Divide both sides by -0.0017104

T=11.81478017 degrees Celsius

It you subs in [T-20] as -8.185 into either equation to double check, at T, the resistance will be about 0.485[tex]\Omega[/tex]

6 years late, but hope this helps.

R=R

FYI the figures quote are temperature coefficients measured in K

Where you want the resistance to be equal, you just back the copper and iron halves of the equation together (copper on the left, iron on the right).

0.501 [1 + 0.0039 (T - 20)] = 0.487 [1 + 0.0005 (T - 20)]

Multiply the lot out, so as to separate T

0.501 + 0.0019539T - 0.039078 = 0.487 + 0.0002435T - 0.00487

Real numbers on the left, expressions in T on the right

0.501 - 0.487 - 0.039078 + 0.00487 = (0.0002435 - 0.0019539)T

-0.020208 = -0.0017104T

Divide both sides by -0.0017104

T=11.81478017 degrees Celsius

It you subs in [T-20] as -8.185 into either equation to double check, at T, the resistance will be about 0.485[tex]\Omega[/tex]

6 years late, but hope this helps.

Last edited:

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