In the circuit shown $P \ne R$, the reading of the galvanometer is same with switch $S$ open or closed. Then

What are the advantages of the null-point method in a Wheatstone bridge ? What additional measurements would be required to calculate ${{\rm{R}}_{{\rm{unknown}}}}$ by any other method ?

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

If in the experiment of Wheatstone's bridge, the positions of cells and galvanometer are interchanged, then balance points will

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