The potentiometer is best for measuring voltage, as:

1. It has a sensitive galvanometer
2. It has wire of high resistance
3. It measures p.d. like in closed circuit
4. It measures p.d. like in open circuit

If the specific resistance of a potentiometer wire is ${10}^{-7}$ $\Omega m$ and the current flow through it is 0.1 A, the cross-sectional area of the wire is  ${10}^{-6}$ $m^2$, then potential gradient will be:

1. ${10}^{-2}$ $V/m$

2. ${10}^{-4}$ $V/m$

3. ${10}^{-6}$ $V/m$

4. ${10}^{-8}$ $V/m$