Resistor analog: Marbles cascading down pin board.

Resistor analog: marble bounce off nails. This demonstration is an analog of electrical conduction in a resistive material. The marbles (analog of the charge carriers) move under the influence of gravity (analog of the electric field) down the inclined plane. After moving a short distance the marble collides (i.e. scatters) with one of the nails (an impurity in the metal) losing some of its energy. On average the marble moves down the plane with some average drift velocity. The current of marbles can only be sustained if the lecturer acts as a battery and continually lifts the marbles up to the top of the board thus replacing the energy which has been dissipated in the collisions. It can be mentioned that the nails presumably are heated by the collisions, the analog of Joule heating. Adjusting the tilt of the board is the analog of varying the electric field. Small tilt angles give slow drift velocity and vice-versa.