The neutral temperature of a thermocouple is defined as the temperature at which:

Four resistances $10 \ \Omega$,$5 \ \Omega$,$7 \ \Omega$ and $3 \ \Omega$ are connected to form the sides of a rectangle $AB$,$BC$,$CD$,and $DA$ respectively. Another resistance of $10 \ \Omega$ is connected across the diagonal $AC$. The equivalent resistance between $A$ and $B$ is ............. $\Omega$.

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:

Two infinite circuits (shown below) are called 'Circuit $A$' and 'Circuit $B$'. The equivalent resistance of 'Circuit $A$' is $x$ and that of 'Circuit $B$' is $y$ between terminals $1$ and $2$.

$A$ cell of emf $1.8 \ V$ gives a current of $17 \ A$ when directly connected to an ammeter of resistance $0.06 \ \Omega$. The internal resistance of the cell is: (in $\Omega$)

The resistance between points $A$ and $B$ is