First, however, we'll look at a simple circuit composed of only resistors as shown in Figure 4.
Figure 4: Voltage Divider
In this circuit, we'll assume that no current flows out of the tap between the two resistors. (This assumption, as many in engineering are, is not always justifiable. We simply keep that in mind and correct for any inaccuracies if they are significant.) Given that assumption, we can see that the current through both resistors is equal and is . The output voltage is then given by v=iR which in this case gives
Notice that the constant by which we are performing multiplication is strictly less than one. This restriction is not present in the next computational circuit.
We can create an adjustable voltage divider by using a potentiometer which is usually implemented by a strip of carbon with a wiper. The ends of the resistive strip are connected to the voltage we want to divide. Then the wiper becomes the point between our two resistors and gives a voltage proportional to the voltage to be divided and to the fraction of the strip which is ``below'' the wiper.