Alistair Thomson
Forum Participant

The resistor voltage divider works because when two resistors are connected in series and you connect a voltage to one end of the series pair, and another voltage to the other end, the junction between these resistors will have a voltage somewhere between the two outside voltages. For a 50/50 divider, you make both resistors the same value and the middle voltage will be exactly half-way between the two applied voltages.

Actually, that needs some further information! The theory only works if both resistors have the same current going through them, so it is important that when you are tapping the 50% voltage, you don’t take much current, otherwise one of the resistor pair will be drawing more current than the other one, and that will change the middle voltage. That means that the thing you connect to the junction must have a very high impedance – like most terminals on a tube.