which has a zero thermal coefficient of resistance. To do this

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It is desired to make a 20 Ω coil of wire, which has a zero thermal coefficient of resistance. To do this, a carbon resitor fo resistane R1 is placed in series with an iron resistor of resistance R2 the proportions of iron and carbon are so chosen that R1+R2=20Ω for all temperatures near 20∘C. How long are R1 and R2? αcarbon =− 0.5 × 10^−3.∘ C−1 , α iron = 5×10^−3.∘C(−1)
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Nov
It is desired to make a 20 Ω coil of wire, which has a zero thermal coefficient of resistance. To do this, a carbon resitor fo resistane R1 is placed in series with an iron resistor of resistance R2 the proportions of iron and carbon are so chosen that R1+R2=20Ω for all temperatures near 20∘C. [...]
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