Two wires $$A$$ and $$B$$ of equal lengths are connected in left and right gap of a meter bridge, null point is obtained at $$40 \mathrm{~cm}$$ from left end. Diameters of the wire $$A$$ and $$B$$ are in that ratio $$3: 1$$. The ratio of specific resistance of $$A$$ to the of $$B$$ is

A potentiometer wire is $$4 \mathrm{~m}$$ long and potential difference of $$3 \mathrm{~V}$$ is maintained between the ends. The emf of the cell, which balances against a length of $$100 \mathrm{~cm}$$ of the potentiometer wire is