What are they - they can be used to split the voltage of a circuit. They are widely used in electronic circuits for setting and adjusting voltages - e.g. in radios, games and toys. You may find that you need a supply of 6 volts and you have a 9 volt battery, your only option may be to make a potential divider. When two resistors of equal value (e.g. 1K) are connected across a supply, current will flow through them. If a meter is placed across the supply shown in the diagram it will register 9v. If the meter is then placed between the 0v and the middle of the two resistors it will read 4.5v. The battery voltage has been divided in half.
If the resistor values are changed to 2K and 1K the voltage will be 6v. The voltage at the centre is determined by the ratio of the two resistor values and is given by the formula: