First, the 3-D model (Figure 2) can be drawn on the blackboard. The height of the
battery shows the amount by which the electric potential has been increased. Similarly, the height of the resistors illustrates the voltage drop on them. Since the positive terminal of the battery and the top of resistor R1, are at the same height, electric potentials at these points are equal. Similarly, since they are situated at the same height, the base of R1 and the top of the R2, have the same electric potentials. Using the same approach, one can easily see that the base of R2 and the negative terminal of the battery are at the same height and hence, have the
same electric potentials.