Potential Divider Circuits

Voltage is 'shared out' across resistors according to their resistance value. The bigger the resistance of a resstor compared to others sharing the voltage, the bigger the share it will get.

In a practical situation we can make use of this potential division to produce a variale power supply from one of fixed voltage. To do this we can use a potentiometer.

A potentiometer is often referred to by electronic engineers as a 'pot', is a three-terminal resistor with a sliding contact that can be used as an adjustable voltage divider. If only two terminals are used, one end (A or B) and 'the wiper'(W), it acts as a variable resistor or rheostat. Potentiometers are commonly used to control electrical devices such as volume controls on audio equipment. They are operated by a mechanism that means that can be used as position transducers, for example, in a joystick.

In school you will often use a rheostat to produce a potential divider circuit.

Remember that voltage is shared by resistors. R_L (load resotance) will therefore get the same voltage as R₂. If the slider is half way the voltage across R_L will be half the batter potential. The ratio of voltgae V_T to the total resistance will be the same as the voltage V_L to the load resistance.

Therefore if you only require 6V but have a 12V battery, you can 'tap off' the required 6V by using a potential divider ('pot') arrangement with the 'wiper' at a half way position - by making R_L half of R_T.