Potential difference between the points P and Q is nearly

In potentiometer experiments, two cells of e. m. f. '$$E_1$$' and '$$E_2$$' are connected in series $$\left(E_1>E_2\right)$$, the balancing length is $$64 \mathrm{~cm}$$ of the wire. If the polarity of $$E_2$$ is reversed, the balancing length becomes $$32 \mathrm{~cm}$$. The ratio $$\mathrm{E}_1 / \mathrm{E}_2$$ is

In meter bridge experiment, null point was obtained at a distance '$$l$$' from left end. The values of resistances in the left and right gap are doubled and then interchanged. The new position of the null point is

A galvanometer has resistance '$$\mathrm{G}$$' and range '$$\mathrm{V} g$$'. How much resistance is required to read voltage upto '$$\mathrm{V}$$' volt?