In the circuit shown, the current in $4\Omega$  resistance is 1.2A. What is the potential difference (in volt) between B and C?

Potential difference across the $4\Omega$  resistance $=1.2\times 4=4.8\mathrm{V}$
Potential difference across the $8\Omega$  resistance =4.8V

$i_2=\frac{4.8}{8}=0.6\mathrm{A}$
$\begin{array}{l}\therefore i=i_1+i_2=1.2+0.6\\ \Rightarrow i=1.8\mathrm{A}\\ \therefore V_{BC}=2\times 1.8=3.6\mathrm{V}\end{array}$