In an experiment on measurements of emf of a cell by a potentiometer, the balancing length for a cell of emf $\mathrm{E}$ and internal resistance $\mathrm{r}$ is found to be $l$. Now if another cell of emf $\mathrm{E}$ and internal resistance $2\mathrm{r}$ is connected in parallel to the first cell and balancing length determined, then the balancing length will be-