$10$ identical cells,each of potential $E$ and internal resistance $r$,are connected in series to form a closed circuit. What is the potential difference across any $3$ cells (in $E$)?

$A$ cell sends a current through a resistance $R$ for time $t$. Now the same cell sends current through another resistance $r$ for the same time. If the same amount of heat is developed in both the resistances,then the internal resistance of the cell is:

Write the equation for the equivalent electromotive force (emf) of a series connection of cells.

$12$ cells,each having the same emf $E$ and internal resistance $r$,are connected in series and kept in a closed box. Some of the cells are wrongly connected. This battery is connected in series with an ammeter and two cells,each identical to the previous cells. The current is $3 \, A$ when the external cells aid the battery and $2 \, A$ when the external cells oppose the battery. How many cells in the battery are wrongly connected?

Four identical cells,each having an electromotive force $(e.m.f.)$ of $12\,V$,are connected in parallel. The resultant electromotive force $(e.m.f.)$ of the combination is .............. $V$.

Two identical cells give the same current through an external resistance of $2 \Omega$ regardless of whether the cells are connected in series or in parallel. The internal resistance of each cell is: (in $Omega$)