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.....................................................................................