Question:
The resistances of an iron wire and a copper wire at $20^{\circ} \mathrm{C}$ are $3.9 \Omega$ and $4.1 \Omega$ respectively. At what temperature will the resistances be equal? Temperature coefficient of resistivity for iron is $5.0 \times 10^{-3} \mathrm{~K}^{-1}$ and for copper it is $4.0 \times 10^{-3} \mathrm{~K}^{-1}$. Neglect any thermal expansion.
Solution:
