In a meter bridge experiment,initially the jockey is at the null point. Now,resistances $R_1$ and $R_2$ are interchanged. The shift in the position of the jockey is ................ $cm$.

$STATEMENT-1$: In a Meter Bridge experiment,a null point for an unknown resistance is measured. Now,the unknown resistance is placed inside an enclosure maintained at a higher temperature. The null point can be obtained at the same point as before by decreasing the value of the standard resistance.
$STATEMENT-2$: The resistance of a metal increases with an increase in temperature.

$A$ student obtained the following observations in an experiment of a meter bridge to find the unknown resistance of the circuit. The most accurate value of the unknown resistance is ............ $\Omega$.

$S.No.$	$R$	$l$	$100-l$	$S = \left( \frac{100-l}{l} \right)R$
$1$	$20\,\Omega$	$43$	$57$	$26.51\,\Omega$
$2$	$30\,\Omega$	$51$	$49$	$28.82\,\Omega$
$3$	$40\,\Omega$	$59$	$41$	$27.80\,\Omega$
$4$	$60\,\Omega$	$70$	$30$	$25.71\,\Omega$

$A$ resistance of $20 \Omega$ is connected in the left gap of a metre bridge and an unknown resistance greater than $20 \Omega$ is connected in the right gap. When these resistances are interchanged,the balance point shifts by $20 \text{ cm}$. The unknown resistance is (in $\Omega$)

The resistance of the meter bridge wire $AB$ in the given figure is $4\,\Omega$. With a cell of emf $\varepsilon_1 = 0.5\,\text{V}$ and rheostat resistance $R_{h1} = 2\,\Omega$,the null point is obtained at point $J$. When the cell is replaced by another one of emf $\varepsilon_2$,the same null point $J$ is found for $R_{h2} = 6\,\Omega$. The emf $\varepsilon_2$ is ................. $\text{V}$.

The resistances in the two gaps of a balanced meter bridge are $X \ \Omega$ and $3X \ \Omega$ respectively. If the resistances are interchanged, the balance point shifts by: (in $\text{ cm}$)