$A$ total of $100$ cells,each having an $emf$ of $5\,V$ and an internal resistance of $1\,\Omega$,are connected to an external resistance of $25\,\Omega$ to obtain the maximum current. If each row contains an equal number of cells,what should be the number of rows?

Twelve cells,each having emf $E$ volts,are connected in series and are kept in a closed box. Some of these cells are wrongly connected with positive and negative terminals reversed. This $12$-cell battery is connected in series with an ammeter,an external resistance $R$ ohms,and a two-cell battery (two cells of the same type used earlier,connected perfectly in series). The current in the circuit when the $12$-cell battery and $2$-cell battery aid each other is $3 \text{ A}$,and it is $2 \text{ A}$ when they oppose each other. Then,the number of cells in the $12$-cell battery that are connected wrongly is:

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 ............ $\Omega$.

$A$ circuit of resistance $R$ is connected to $n$ similar cells. If the current in the circuit is the same when the cells are connected in series or in parallel,and the internal resistance of each cell is $r$,then:

In the network shown,the potential difference between $A$ and $B$ is ................. $V$ $(R = r_1 = r_2 = r_3 = 1 \Omega, E_1 = 3 \, V, E_2 = 2 \, V, E_3 = 1 \, V)$.

$A$ primary cell has an $e.m.f.$ of $1.5\,V$. When short-circuited,it gives a current of $3\,A$. The internal resistance of the cell is ............. $\Omega$.