A slide-wire potentiometer is shown in the figure. In this device the resistances `R_1` and `R_2` of figure are actually a uniform wire `1.000 m` in length. Hence, the resistance `R_1` is alphaortional to length `L_1` and the resistance `R_2` is alphaortional to the length `L_2`. the galvanometer junction `N'` in the figure is sharp-edged key that can slide along the wire and be made to make contact with ot at any position along its length. When a standard cell with an emf of `1.6 V` is used and the switch `S` is in position `A`, the length `L_1` is `40 cm` for no current to flow through the galvanometer. When the switch is moved to position `B`, the length `L_1` must be changed to `60 cm` for tge galvanometer to carry no current. What is the value of the emf `E_2` ?

Explanation

`(E_1)/(E_2) = (l_1)/(l_2)`
`(1.6)/(E_2) = (40)/(60) rArr E_2 = 2.4 V`.