A potentiometer wire of length 1 m is connected to a driver cell of emf 3 V as shown in the figure. When a cell of 1.5 V emf is used in the secondary circuit, the balance point is found to be 60 cm. On replacing this cell and using a cell of unknown emf, the balance point to 80 cm.
(i) Calculate unknown emf of the cell.
(ii) Explain with reason, whether the circuit works, if the drive cell is reprlaced with a cell emf 1 V.
(iii) Does the high resistance R, used in the secondary circuit affrct the balance point? Justify your answer.

Explanation

(i) Given, AB= 1m
For balanced condition `rArr (epsi_(1))/(epsi_(2)) = (l_(1))/(l_(2)) = (60)/(80)`
`rArr epsi_(2) = 2V`
(ii) No, the emf of driver cell must be greater than the emf of secondary cell.
(iii) No, it does not affect the balance point, because no current flows through it, when jockey touches balance point.