In the circuit shown,the point '$B$' is earthed. The potential at the point '$A$' is ............. $V$.

The diagram shows a circuit used in an experiment to determine the $emf$ $(E)$ and internal resistance $(r)$ of the cell $C$. $A$ graph was plotted of the potential difference $V$ between the terminals of the cell against the current $I$,which was varied by adjusting the rheostat. The graph is shown on the right; $x$ and $y$ are the intercepts of the graph with the axes as shown. What is the internal resistance of the cell?

For the previous objective,which of the following graphs is correct?

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 ................ $W$.

Two resistors $400 \, \Omega$ and $800 \, \Omega$ are connected in series across a $6 \, V$ battery. The potential difference measured by a voltmeter of $10 \, k \Omega$ connected across the $400 \, \Omega$ resistor is close to $.... \, V$.

$P$ and $Q$ are two identical wires of resistance $2000\, \Omega$ each, and $M$ is the midpoint of $PQ$. A voltmeter of resistance $1000\, \Omega$ is connected between $P$ and $M$. When a potential difference of $150\, V$ is applied across $PQ$, the reading of the voltmeter will be ............. $V$.