Bboth length and radius of wire are doubled
b
$R=\frac{\rho \ell}{\pi r^{2}}$
When $\ell$ is $\frac{\ell}{2}$ and radius is $\frac{\mathrm{r}}{2}$
$\therefore \quad \mathrm{R}^{\prime}=\frac{\rho \ell{4}}{\pi 2 \mathrm{r}^{2}}=\frac{2 \rho \ell}{\pi \mathrm{r}^{2}}$
So, $\mathrm{R}^{\prime}=2 \mathrm{R}$ So, heat is doubled according to $\mathrm{H}=\mathrm{I}^{2} \mathrm{RT}$