In potentiometer experiment, cells of e.m.f. $E_1$ and $E_2$ are connected in series $\left(E_1>E_2\right)$ the balancing length is 80 cm of the wire. If the polarity of $E_2$ is reversed, the balancing length becomes 20 cm. The ratio $\mathrm{E}_1 / \mathrm{E}_2$ is

In the circuit, current flowing through the circuit is

Two identical galvanometers are converted into voltmeter and millivoltmeter. As compared to the series resistance of voltmeter, the series resistance of millivoltmeter will be

Potential difference between the points A and B is nearly