What equal length of an iron wire and a copper-nickel alloy wire, each of \( 2 \text{mm} \) diameter connected parallel to give an equivalent resistance of \( 3 \Omega \)? (Given resistivities of iron and copper-nickel alloy wire are \( 12 \mu\Omega \text{cm} \) and \( 51 \mu\Omega \text{cm} \) respectively).
