This demo consists of a wooden panel, upon which are mounted a fixed resistance R1 and variable resistance R2, wired in series. The voltage (V) drop across R1 and the current (A) flowing through R1 and R2 can be measured by two reflection meters. R2 is provided to adjust the current in the circuit to any given value so that a number of determinations may be made of A and V. These values may be plotted on the blackboard.