In the following circuit,the terminal voltage across the cell is (in $V$)

Two resistances of $400 \Omega$ and $800 \Omega$ are connected in series with a $6 \text{ V}$ battery of negligible internal resistance. $A$ voltmeter of resistance $10000 \Omega$ is used to measure the potential difference across the $400 \Omega$ resistor. The error in the measurement of potential difference in volts is approximately:

The sliding contact $C$ is at one-fourth of the length of the potentiometer wire $(AB)$ from $A$ as shown in the circuit diagram. If the resistance of the wire $AB$ is $R_0$,then the potential drop $(V)$ across the resistor $R$ is

$A$ potential divider circuit is shown in the figure. The output voltage $V_0$ is

In the figure,the value of the resistor to be connected between $C$ and $D$ so that the equivalent resistance of the entire circuit between $A$ and $B$ does not change with the number of elementary sets used is

In the following circuit diagram,$E = 4\,V, r = 1\,\Omega$ and $R = 45\, \Omega$,then the reading of the ammeter $A$ will be