If the potential difference between points B and D is zero in the given circuit, the value of x is $\dfrac{1}{n}\ \Omega$. The value n is

A potentiometer wire is 4m long and potential difference of 3V is maintained between the ends. The e.m.f. of the cell which balances against a length of 100 cm of the potentiometer wire is

A metre bridge experiment, the resistance in the left gap is $20\ \Omega$ and in the right gap is $60\ \Omega$. The bridge is balanced. The distance of the null point from the centre of the wire is

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