Question

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 shifts to 80 cm.

(i) Calculate unknown emf of the cell.

(ii) Explain with reason, whether the circuit works, if the driver cell is replaced with a cell of emf 1 V.

(iii) Does the high resistance R, used in the secondary circuit affect the balance point? Justify our answer.

Answer 1

(i)

(ii) The circuit will not work if emf of driver cell is 1 V (less than that of cell in secondary circuit), because total voltage across wire AB is 1 V which cannot balance the voltage V.

(iii) No, since at balance point no current flows through galvanometer G i.e., cell remains in open circuit.