A wire of length $L$ and $3$ identical cells of negligible internal resistances are connected in series. Due to the current, the temperature of the wire is raised by $\Delta T$ in a time $t$. A number $N$ of similar cells are now connected in series with a wire of the same material and cross-section but of length $2L$. The temperature is raised by the same amount $\Delta T$ in the same time. The value of $N$ is

Question

$\begin {array} {1 1} (A)\;4 \\ (B)\;6 \\ (C)\;Non-integral\: answer. \: The \: described\: situation\: is\: not \: possible \\ (D)\;None \: of \: these \end {array}$