
Potential difference between $A$ and $B$ ${V_A} - {V_B} = 2 \times 12$
$ \Rightarrow $ ${V_A} - 0 = 24\,V$ $ \Rightarrow $ ${V_A} = 24\,V$

(Given resistivities of iron and copper-nickel alloy wire are $12 \;\mu \Omega {cm}$ and $51\; \mu \Omega {cm}$ respectively) (in ${m}$)



