A copper wire and an iron wire, each having an area of cross–section A and lengths L₁ and L₂ are joined end to end. The copper end is maintained at a potential V₁ and the iron end at a lower potential V₂. If σ₁ and σ₂ are the conductivities of copper and iron respectively, then the potential of the junction will be?

Here in this question, you write three equations for the potential difference.
Vcopper – Viron= i (Riron + Rcopper) --------(i)
Calculate the value of current from here and put in the lower equation.
Vc – Vjunction = i Rcopper

As we know , R = i/sigma (L/A)
I hope you got the hint, that would help you to find the correct answer.


Good Luck.....................................................................................