When current supplied by a cell to a circuit is $0.3 \,A$,its terminal potential difference is $0.9 \,V$. When the current supplied becomes $0.25 \,A$,its terminal potential difference becomes $1.0 \,V$. The internal resistance of the cell is ............ $\Omega$.

Two cells $E_1$ and $E_2$ having equal $EMF$ $E$ and internal resistances $r_1$ and $r_2$ $(r_1 > r_2)$ respectively are connected in series. This combination is connected to an external resistance $R$. It is observed that the potential difference across the cell $E_1$ becomes zero. The value of $R$ will be

Two cells of same emf $E$ but different internal resistances $r_{1}$ and $r_{2}$ are connected in series with a resistance $R$. The value of resistance $R$,for which the potential difference across the second cell is zero,is

Five identical cells each of internal resistance $1\, \Omega$ and $emf$ $5\, V$ are connected in series and in parallel with an external resistance $R$. For what value of $R$ will the current in the series and parallel combination remain the same? (in $\Omega$)

One electric cell (having emf of $2 \ V$ and internal resistance of $0.1 \ \Omega$) and another electric cell (having emf of $4 \ V$ and internal resistance of $0.2 \ \Omega$) are connected in parallel to each other. The equivalent emf will be . . . . . . $V$.

$32$ cells,each of $emf$ $3V$,are connected in series and kept in a box. Externally,the combination shows an $emf$ of $84V$. The number of cells reversed in the combination is