Potential divider circuits

A potential divider is a circuit with several resistors in series connected across a voltage source, used to produce a required fraction of the source potential difference, which remains constant.

You can also make a potential divider supply a variable potential difference by using a variable resistor as one of the resistors in series, therefore by varying the resistance across it, you can vary the potential difference output. For example, if the resistance across R1 increases, the output p.d will decrease as circuit current has decreased and V=IR.