" of is the emf of a cell is "

Where does the emf of a cell exist?

Remya makes the following circuit to measure the emf of a cell. She says that the voltmeter reading will give the emf of the cell.The Physics teacher says that it is not possible to measure the emf of the cell in this way. Justify this statement.

For the working of potentiometer, the emf of cell in the primary circuit (E) compared to the emf of the cell in the secondary circuit (E^(1)) is