Find the voltage $V_2$ across $R_2$ for the given circuit. (in $V$)

$A$ cell of emf $6\, V$ and internal resistance $0.5\, \Omega$ is short-circuited. The current in the cell is ............... $A$.

The readings of the voltmeter and ammeter in the circuit shown in the diagram are respectively

Two equal resistances,$400 \Omega$ each,are connected in series with an $8 V$ battery. If the resistance of the first one increases by $0.5 \%$,what is the change required in the resistance of the second one in order to keep the potential difference across it unaltered?

In the given circuit,the internal resistance of the $18\,V$ cell is negligible. If $R_1 = 400\,\Omega$,$R_3 = 100\,\Omega$,and $R_4 = 500\,\Omega$,and the reading of an ideal voltmeter across $R_4$ is $5\,V$,then the value of $R_2$ will be ........... $\Omega$.

When a battery sends an electric current through a resistor $R_1$ for time $t$,the heat produced in the resistor is $Q$. When the same battery sends an electric current through a resistor $R_2$ for the same time $t$,the heat produced in the resistor $R_2$ is also $Q$. Determine the internal resistance $r$ of the battery.