In the circuit shown,the readings of the ammeter and voltmeter are $4\,\, A$ and $20\,\, V$ respectively. The meters are non-ideal. Then $R$ is

Three identical batteries are connected in series with a wire of length $L$. The temperature of the wire increases by $T$ in time $t$. If $N$ such batteries are connected in series with a wire of the same material but length $2L$,the temperature increases by the same amount $T$ in the same time $t$. Find the value of $N$.

$A$ current of $6 \ A$ enters one corner $P$ of an equilateral triangle $PQR$ having three wires of resistance $2 \ \Omega$ each and leaves by the corner $R$ as shown in the figure. Then the currents $I_1$ and $I_2$ are respectively:

The series combination of two batteries,both of the same emf $10 \; V,$ but different internal resistances of $20 \; \Omega$ and $5 \; \Omega,$ is connected to the parallel combination of two resistors $30 \; \Omega$ and $R \; \Omega.$ If the voltage difference across the battery of internal resistance $20 \; \Omega$ is zero,the value of $R$ (in $\Omega$) is:

When a current of $2 \ A$ flows through a conductor,$80 \ J$ of heat is produced in $10 \ s$. The resistance of the conductor is ........... $\Omega$.

The reading of the ammeter in the following figure will be: (in $\text{A}$)