The potential difference between points $A$ and $B$ of the adjoining figure is

$A$ battery with an internal resistance of $4\,\Omega$ is connected to a circuit as shown in the figure. For the circuit to receive maximum power,the value of $R$ should be ..... $\Omega$.

$A$ voltmeter is connected in parallel with a variable resistance $R$ which is in series with an ammeter and a cell as shown in the figure. For one value of $R$,the meters read $0.3 \, A$ and $0.9 \, V$. For another value of $R$,the readings are $0.25 \, A$ and $1.0 \, V$. What is the internal resistance of the cell in $\Omega$?

The reading of the voltmeter in the circuit shown is ............. $V$. (in $.25$)

Two resistors of $6\,\Omega$ and $9\,\Omega$ are connected in series to a $120\,V$ source. The power consumed by the $6\,\Omega$ resistor is ........... $W$.

Three resistors of $4\,\Omega$,$6\,\Omega$,and $12\,\Omega$ are connected in parallel,and the combination is connected in series with a $1.5\,V$ battery of $1\,\Omega$ internal resistance. The rate of Joule heating in the $4\,\Omega$ resistor is ................ $W$.