A potentiometer PQ is set up to compare two resistances as shown in the figure. The ammeter A in the circuit reads 1.0 A when two way key K_3 is…

A potentiometer PQ is set up to compare two resistances as shown in the figure. The ammeter A in the circuit reads $\displaystyle 1.0$ A when two way key $\displaystyle \mathrm{K}_3$ is open. The balance point is at a length $\displaystyle l_1 \mathrm{~cm}$ from P when two way key $\displaystyle \mathrm{K}_3$ is plugged in between $\displaystyle 2$ and $\displaystyle 1$, while the balance point is at a length $\displaystyle l_2 \mathrm{~cm}$ from P when key $\displaystyle K_3$ is plugged in between $\displaystyle 3$ and 1. The ratio of two resistances $\displaystyle \frac{\mathrm{R}_1}{\mathrm{R}_2}$, is found to be :