In a meter bridge experiment,the balance point is obtained if the gaps are closed by $2\,\Omega$ and $3\,\Omega$ resistors. $A$ shunt of $x\,\Omega$ is added to the $3\,\Omega$ resistor to shift the balancing point by $22.5\,cm$. The value of $x$ is $................$

When two resistances $R_1$ and $R_2$ are connected in series and introduced into the left gap of a meter bridge and a resistance of $10 \ \Omega$ is introduced into the right gap,a null point is found at $60 \ cm$ from the left side. When $R_1$ and $R_2$ are connected in parallel and introduced into the left gap,a resistance of $3 \ \Omega$ is introduced into the right gap to get a null point at $40 \ cm$ from the left end. The product $R_1 R_2$ is $............. \ \Omega$.

Shown in the figure below is a meter-bridge set up with null deflection in the galvanometer. The value of the unknown resistor $R$ is ............. $\Omega$.

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 . . . . $\Omega$.

Explain how the value of an unknown resistor can be obtained by using a meter bridge.

In a meter bridge,the point $D$ is the neutral point (null point) as shown in the figure.