In the meter bridge experiment,for given values of $R_1$ and $R_2$,the balance point is $20 \ cm$ from point $A$. When $R_2$ is shunted by a $20 \ \Omega$ resistance,the balancing point shifts to $50 \ cm$ from point $A$. Find the value of $R_2$ in $\Omega$.

In a meter bridge,the balancing length from the left end (standard resistance of $1 \, \Omega$ is in the right gap) is found to be $20 \, cm$. The value of the unknown resistance is ............... $\Omega$.

Assertion $(A):$ In a meter bridge experiment,the unknown resistance is placed inside an enclosure maintained at a higher temperature. The null point can be obtained at the same position as before by decreasing the value of the standard resistance.
Reason $(R):$ The resistance of a metal increases with an increase in temperature.

$A$ resistance of $2 \Omega$ is connected across one gap of a metre-bridge (the length of the wire is $100 \text{ cm}$) and an unknown resistance,greater than $2 \Omega$,is connected across the other gap. When these resistances are interchanged,the balance point shifts by $20 \text{ cm}$. Neglecting any corrections,the unknown resistance is (in $\Omega$)

In a metre bridge experiment,the null point is obtained at $20 \,cm$ from the left end of the wire,when resistance $X$ is balanced against another resistance $Y$ $(X < Y)$. To balance a resistance $4X$ against $Y$,the new position of the null point from the same end will be: (in $\,cm$)

$A$ wire of length $10 \ cm$ and radius $\sqrt{7} \times 10^{-4} \ m$ is connected across the right gap of a meter bridge. When a resistance of $4.5 \ \Omega$ is connected in the left gap using a resistance box,the balance length is found to be at $60 \ cm$ from the left end. If the resistivity of the wire is $R \times 10^{-7} \ \Omega \ m$,then the value of $R$ is: