For the post office box arrangement to determine the value of unknown resistance the unknown resistance should be connected between

In the following diagram the wheat stone bridge is balanced when we interchange the resistances of

In a meter bridge experiment, resistances are connected as shown in the following figure. The balancing length $l_1$ is $55\, cm$. Now, an unknown resistance $x$ is connected in series with $P$ and the new balancing length is found to be $75\, cm$. The value of $x$ is

Three resistances $P, Q, R$ each of $2 \,\,\Omega$ and an unknown resistance $S$ form the four arms of a Wheatstone bridge circuit. When a resistance of $6 \,\,\Omega$ is connected in parallel to $S$ the bridge gets balanced. What is the value of $S\,?$ …………… $\Omega$

The resistance of the meter bridge $AB$ in given figure is $4\,\Omega $. With a cell of emf  $\varepsilon \, = 0.5\,\,V$ and rheostat resistance $R_h = 2\,\Omega $ the null point is obtained at some point $J.$ When the cell is replaced by another one of emf $\varepsilon \, = {\varepsilon _2}$ the same null point $J$ is found for $R_h = 6\,\Omega .$ The $emf$  ${\varepsilon _2}$ is …………….. $V$