sorry for the drawing.Hope you guys can bear with it. The electromotive force can be calculated by opening the switch and the voltmeter will show the exact voltage of the battery. When the switch is closed,there will be a voltage drop due to the internal resistance of the battery. The question is, there will be a potential different across the two points between the battery when the circuit is incomplete which will show the exact voltage of the battery,but does the same goes to reading of the voltage given that the circuit is complete ? Why ? (please refer to the drawing) another question, if there is an internal resistance within the battery why do they requirre the two points ? and why not just connect the voltmeter to the positve and negative terminal of the battery ? Thanks !