The situation I would like to mention here is when the switch is open. From what I have learnt in my reference book, it said that there's no current flowing when the switch is opened and the value of the voltmeter shows is the emf of the cell. Besides, we know there's actually a little of current flowing through the voltmeter which has high resistance otherwise the pointer of voltmeter will not deflect. In other words, what I'm trying to ask are :
- If there's a little current flowing through the voltmeter during the switch is opened, shouldn't that the reading of voltmeter is the potential drops across the cell?
- I noticed that my reference books usually mention "The emf of a cell can be measured approximately by connecting a high resistance voltmeter across the cell as shown in the figure above. The voltmeter reading is approximately the emf, E of the cell.". So why is the value of voltmeter shows is approximately the actually value of emf, could it because the potential drops due to internal resistance of the cell is included?