Figure: A voltmeter is connected across the output terminals of potentiometer

The potentiometer consists of a resistance R_P and its wiper can move from the top position x = x_max to the bottom position x=0. The resistance R_x correspond to the position x of the wiper such that, 

(Supposed that the per unit length resistance of the potentiometer is similar throughout its length). The figure shown above symbolizes a potentiometer whose output is linked to a voltmeter. In true logic, the measurement of the output voltage V_o with a voltmeter is affected by the voltmeter resistance RV and the relationship among Vo and x (i.e., x = wiper distance from the bottom position) can simply be established. We recognize that the voltmeter resistance is very high in M Ω range and practically negligible current is flowing via the voltmeter. Under this situation, one can write the expression for voltage among the wiper and the bottom end terminal of the potentiometer as

It might be noted that based on the position of movable tap terminal the output voltage (V_out ) can be controlled. By regulating the wiper toward the top terminal, we can raise V_out. The opposite effect can be noted whereas the movable tap moves toward the bottom terminal. An easy application of potentiometer in actual practice is the volume control of a radio receiver by regulating the applied voltage to the input of audio amplifier of a radio set. Such audio amplifier boosts this voltage by a certain fixed factor and this voltage is able of driving the loudspeaker.