Resistance in the two gaps of a meter bridge are $10 \, \Omega$ and $30 \, \Omega$ respectively. If the resistances are interchanged, the balance point shifts by .............. $cm$.

$A$ meter bridge is set up as shown to determine the end corrections at $A$ and $B$. When a resistance of $15\,\Omega$ is used in the left gap and $20\,\Omega$ in the right gap,the null point is obtained at a distance of $42\,cm$ from $A$. When these resistances are interchanged,the null point is obtained at a distance of $57\,cm$ from $A$. The values of the end corrections are:

In a metre bridge experiment, the resistance in the left gap is $15 \text{ } \Omega$ and in the right gap is $45 \text{ } \Omega$. The bridge is balanced. The distance of the null point from the centre of the wire is (in $\text{ cm}$)

Resistances are connected in a meter bridge circuit as shown in the figure. The balancing length $l_{1}$ is $40\,cm$. Now an unknown resistance $x$ is connected in series with $P$ and the new balancing length is found to be $80\,cm$ measured from the same end. Then the value of $x$ will be $.......\Omega$.

In order to measure the internal resistance $r_1$ of a cell of emf $E$,a meter bridge of wire resistance $R_0=50 \Omega$,a resistance $R_0/2$,another cell of emf $E/2$ (internal resistance $r$) and a galvanometer $G$ are used in a circuit,as shown in the figure. If the null point is found at $l=72 \text{ cm}$,then the value of $r_1$ is . . . . $\Omega$.

When a wire is connected in the left gap of a metre bridge,the balancing point is at $40 \ cm$ from the left end of the bridge wire. If the wire in the left gap is stretched so that its length is doubled and again connected in the same gap,then the balancing point from the left end of the bridge wire is